diff --git a/codex-rs/Cargo.lock b/codex-rs/Cargo.lock
index 34eeb74612..eccf37e598 100644
--- a/codex-rs/Cargo.lock
+++ b/codex-rs/Cargo.lock
@@ -27,6 +27,12 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f26201604c87b1e01bd3d98f8d5d9a8fcbb815e8cedb41ffccbeb4bf593a35fe"
 
+[[package]]
+name = "adler2"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "512761e0bb2578dd7380c6baaa0f4ce03e84f95e960231d1dec8bf4d7d6e2627"
+
 [[package]]
 name = "ahash"
 version = "0.8.11"
@@ -251,7 +257,7 @@ dependencies = [
  "cc",
  "cfg-if",
  "libc",
- "miniz_oxide",
+ "miniz_oxide 0.7.4",
  "object",
  "rustc-demangle",
 ]
@@ -274,6 +280,15 @@ version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3a8241f3ebb85c056b509d4327ad0358fbbba6ffb340bf388f26350aeda225b1"
 
+[[package]]
+name = "bincode"
+version = "1.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1f45e9417d87227c7a56d22e471c6206462cba514c7590c09aff4cf6d1ddcad"
+dependencies = [
+ "serde",
+]
+
 [[package]]
 name = "bit-set"
 version = "0.5.3"
@@ -622,6 +637,7 @@ dependencies = [
  "tracing-appender",
  "tracing-subscriber",
  "tui-input",
+ "tui-markdown",
  "tui-textarea",
 ]
 
@@ -706,6 +722,15 @@ version = "0.8.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "773648b94d0e5d620f64f280777445740e61fe701025087ec8b57f45c791888b"
 
+[[package]]
+name = "crc32fast"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a97769d94ddab943e4510d138150169a2758b5ef3eb191a9ee688de3e23ef7b3"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "crossbeam-channel"
 version = "0.5.15"
@@ -1151,6 +1176,16 @@ version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0ce7134b9999ecaf8bcd65542e436736ef32ddca1b3e06094cb6ec5755203b80"
 
+[[package]]
+name = "flate2"
+version = "1.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7ced92e76e966ca2fd84c8f7aa01a4aea65b0eb6648d72f7c8f3e2764a67fece"
+dependencies = [
+ "crc32fast",
+ "miniz_oxide 0.8.8",
+]
+
 [[package]]
 name = "float-cmp"
 version = "0.10.0"
@@ -1276,6 +1311,12 @@ version = "0.3.31"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f90f7dce0722e95104fcb095585910c0977252f286e354b5e3bd38902cd99988"
 
+[[package]]
+name = "futures-timer"
+version = "3.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f288b0a4f20f9a56b5d1da57e2227c661b7b16168e2f72365f57b63326e29b24"
+
 [[package]]
 name = "futures-util"
 version = "0.3.31"
@@ -1303,6 +1344,15 @@ dependencies = [
  "byteorder",
 ]
 
+[[package]]
+name = "getopts"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14dbbfd5c71d70241ecf9e6f13737f7b5ce823821063188d7e46c41d371eebd5"
+dependencies = [
+ "unicode-width 0.1.14",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.2.16"
@@ -1332,6 +1382,12 @@ version = "0.28.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4271d37baee1b8c7e4b708028c57d816cf9d2434acb33a549475f78c181f6253"
 
+[[package]]
+name = "glob"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a8d1add55171497b4705a648c6b583acafb01d58050a51727785f0b2c8e0a2b2"
+
 [[package]]
 name = "h2"
 version = "0.4.9"
@@ -1797,6 +1853,15 @@ dependencies = [
  "either",
 ]
 
+[[package]]
+name = "itertools"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b192c782037fadd9cfa75548310488aabdbf3d2da73885b31bd0abd03351285"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itoa"
 version = "1.0.15"
@@ -1901,6 +1966,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "linked-hash-map"
+version = "0.5.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0717cef1bc8b636c6e1c1bbdefc09e6322da8a9321966e8928ef80d20f7f770f"
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.4.15"
@@ -2049,6 +2120,15 @@ dependencies = [
  "adler",
 ]
 
+[[package]]
+name = "miniz_oxide"
+version = "0.8.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3be647b768db090acb35d5ec5db2b0e1f1de11133ca123b9eacf5137868f892a"
+dependencies = [
+ "adler2",
+]
+
 [[package]]
 name = "mio"
 version = "1.0.3"
@@ -2210,6 +2290,28 @@ version = "1.21.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "42f5e15c9953c5e4ccceeb2e7382a716482c34515315f7b03532b8b4e8393d2d"
 
+[[package]]
+name = "onig"
+version = "6.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8c4b31c8722ad9171c6d77d3557db078cab2bd50afcc9d09c8b315c59df8ca4f"
+dependencies = [
+ "bitflags 1.3.2",
+ "libc",
+ "once_cell",
+ "onig_sys",
+]
+
+[[package]]
+name = "onig_sys"
+version = "69.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b829e3d7e9cc74c7e315ee8edb185bf4190da5acde74afd7fc59c35b1f086e7"
+dependencies = [
+ "cc",
+ "pkg-config",
+]
+
 [[package]]
 name = "openssl"
 version = "0.10.72"
@@ -2395,6 +2497,19 @@ version = "0.3.32"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7edddbd0b52d732b21ad9a5fab5c704c14cd949e5e9a1ec5929a24fded1b904c"
 
+[[package]]
+name = "plist"
+version = "1.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eac26e981c03a6e53e0aee43c113e3202f5581d5360dae7bd2c70e800dd0451d"
+dependencies = [
+ "base64 0.22.1",
+ "indexmap 2.9.0",
+ "quick-xml",
+ "serde",
+ "time",
+]
+
 [[package]]
 name = "portable-atomic"
 version = "1.11.0"
@@ -2471,6 +2586,15 @@ dependencies = [
  "yansi",
 ]
 
+[[package]]
+name = "proc-macro-crate"
+version = "3.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "edce586971a4dfaa28950c6f18ed55e0406c1ab88bbce2c6f6293a7aaba73d35"
+dependencies = [
+ "toml_edit",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.95"
@@ -2480,6 +2604,34 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "pulldown-cmark"
+version = "0.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e8bbe1a966bd2f362681a44f6edce3c2310ac21e4d5067a6e7ec396297a6ea0"
+dependencies = [
+ "bitflags 2.9.0",
+ "getopts",
+ "memchr",
+ "pulldown-cmark-escape",
+ "unicase",
+]
+
+[[package]]
+name = "pulldown-cmark-escape"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "007d8adb5ddab6f8e3f491ac63566a7d5002cc7ed73901f72057943fa71ae1ae"
+
+[[package]]
+name = "quick-xml"
+version = "0.32.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d3a6e5838b60e0e8fa7a43f22ade549a37d61f8bdbe636d0d7816191de969c2"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "quote"
 version = "1.0.40"
@@ -2650,6 +2802,12 @@ version = "0.8.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2b15c43186be67a4fd63bee50d0303afffcef381492ebe2c5d87f324e1b8815c"
 
+[[package]]
+name = "relative-path"
+version = "1.9.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba39f3699c378cd8970968dcbff9c43159ea4cfbd88d43c00b22f2ef10a435d2"
+
 [[package]]
 name = "reqwest"
 version = "0.12.15"
@@ -2710,12 +2868,51 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "rstest"
+version = "0.25.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6fc39292f8613e913f7df8fa892b8944ceb47c247b78e1b1ae2f09e019be789d"
+dependencies = [
+ "futures-timer",
+ "futures-util",
+ "rstest_macros",
+ "rustc_version",
+]
+
+[[package]]
+name = "rstest_macros"
+version = "0.25.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1f168d99749d307be9de54d23fd226628d99768225ef08f6ffb52e0182a27746"
+dependencies = [
+ "cfg-if",
+ "glob",
+ "proc-macro-crate",
+ "proc-macro2",
+ "quote",
+ "regex",
+ "relative-path",
+ "rustc_version",
+ "syn 2.0.100",
+ "unicode-ident",
+]
+
 [[package]]
 name = "rustc-demangle"
 version = "0.1.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "719b953e2095829ee67db738b3bfa9fa368c94900df327b3f07fe6e794d2fe1f"
 
+[[package]]
+name = "rustc_version"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cfcb3a22ef46e85b45de6ee7e79d063319ebb6594faafcf1c225ea92ab6e9b92"
+dependencies = [
+ "semver",
+]
+
 [[package]]
 name = "rustix"
 version = "0.38.44"
@@ -2815,6 +3012,15 @@ version = "1.0.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "28d3b2b1366ec20994f1fd18c3c594f05c5dd4bc44d8bb0c1c632c8d6829481f"
 
+[[package]]
+name = "same-file"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "93fc1dc3aaa9bfed95e02e6eadabb4baf7e3078b0bd1b4d7b6b0b68378900502"
+dependencies = [
+ "winapi-util",
+]
+
 [[package]]
 name = "schannel"
 version = "0.1.27"
@@ -2928,6 +3134,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "semver"
+version = "1.0.26"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56e6fa9c48d24d85fb3de5ad847117517440f6beceb7798af16b4a87d616b8d0"
+
 [[package]]
 name = "serde"
 version = "1.0.219"
@@ -3324,6 +3536,28 @@ dependencies = [
  "syn 2.0.100",
 ]
 
+[[package]]
+name = "syntect"
+version = "5.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "874dcfa363995604333cf947ae9f751ca3af4522c60886774c4963943b4746b1"
+dependencies = [
+ "bincode",
+ "bitflags 1.3.2",
+ "flate2",
+ "fnv",
+ "once_cell",
+ "onig",
+ "plist",
+ "regex-syntax 0.8.5",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "thiserror 1.0.69",
+ "walkdir",
+ "yaml-rust",
+]
+
 [[package]]
 name = "system-configuration"
 version = "0.6.1"
@@ -3746,6 +3980,22 @@ dependencies = [
  "unicode-width 0.2.0",
 ]
 
+[[package]]
+name = "tui-markdown"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf47229087fc49650d095a910a56aaf10c1c64181d042d2c2ba46fc3746ff534"
+dependencies = [
+ "ansi-to-tui",
+ "itertools 0.14.0",
+ "pretty_assertions",
+ "pulldown-cmark",
+ "ratatui",
+ "rstest",
+ "syntect",
+ "tracing",
+]
+
 [[package]]
 name = "tui-textarea"
 version = "0.7.0"
@@ -3876,6 +4126,16 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "walkdir"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29790946404f91d9c5d06f9874efddea1dc06c5efe94541a7d6863108e3a5e4b"
+dependencies = [
+ "same-file",
+ "winapi-util",
+]
+
 [[package]]
 name = "want"
 version = "0.3.1"
@@ -4010,6 +4270,15 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
 
+[[package]]
+name = "winapi-util"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf221c93e13a30d793f7645a0e7762c55d169dbb0a49671918a2319d289b10bb"
+dependencies = [
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "winapi-x86_64-pc-windows-gnu"
 version = "0.4.0"
@@ -4295,6 +4564,15 @@ version = "0.5.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1e9df38ee2d2c3c5948ea468a8406ff0db0b29ae1ffde1bcf20ef305bcc95c51"
 
+[[package]]
+name = "yaml-rust"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56c1936c4cc7a1c9ab21a1ebb602eb942ba868cbd44a99cb7cdc5892335e1c85"
+dependencies = [
+ "linked-hash-map",
+]
+
 [[package]]
 name = "yansi"
 version = "1.0.1"
diff --git a/codex-rs/tui/Cargo.toml b/codex-rs/tui/Cargo.toml
index c6b74bbe98..53fd53db30 100644
--- a/codex-rs/tui/Cargo.toml
+++ b/codex-rs/tui/Cargo.toml
@@ -37,4 +37,5 @@ tracing = { version = "0.1.41", features = ["log"] }
 tracing-appender = "0.2.3"
 tracing-subscriber = { version = "0.3.19", features = ["env-filter"] }
 tui-input = "0.11.1"
+tui-markdown = "0.3.3"
 tui-textarea = "0.7.0"
diff --git a/codex-rs/tui/src/history_cell.rs b/codex-rs/tui/src/history_cell.rs
index 92859af286..3693ab53be 100644
--- a/codex-rs/tui/src/history_cell.rs
+++ b/codex-rs/tui/src/history_cell.rs
@@ -96,7 +96,30 @@ impl HistoryCell {
     pub(crate) fn new_agent_message(message: String) -> Self {
         let mut lines: Vec<Line<'static>> = Vec::new();
         lines.push(Line::from("codex".magenta().bold()));
-        lines.extend(message.lines().map(|l| Line::from(l.to_string())));
+        let markdown = tui_markdown::from_str(&message);
+
+        // `tui_markdown` returns a `ratatui::text::Text` where every `Line` borrows from the
+        // input `message` string. Since the `HistoryCell` stores its lines with a `'static`
+        // lifetime we must create an **owned** copy of each line so that it is no longer tied to
+        // `message`. We do this by cloning the content of every `Span` into an owned `String`.
+
+        for borrowed_line in markdown.lines {
+            let mut owned_spans = Vec::with_capacity(borrowed_line.spans.len());
+            for span in &borrowed_line.spans {
+                // Create a new owned String for the span's content to break the lifetime link.
+                let owned_span = RtSpan::styled(span.content.to_string(), span.style);
+                owned_spans.push(owned_span);
+            }
+
+            let owned_line: Line<'static> = Line::from(owned_spans).style(borrowed_line.style);
+            // Preserve alignment if it was set on the source line.
+            let owned_line = match borrowed_line.alignment {
+                Some(alignment) => owned_line.alignment(alignment),
+                None => owned_line,
+            };
+
+            lines.push(owned_line);
+        }
         lines.push(Line::from(""));
 
         HistoryCell::AgentMessage { lines }