diff --git a/crates/uv-client/src/base_client.rs b/crates/uv-client/src/base_client.rs
index 81c78e145..4df6bd475 100644
--- a/crates/uv-client/src/base_client.rs
+++ b/crates/uv-client/src/base_client.rs
@@ -85,6 +85,8 @@ pub struct BaseClientBuilder<'a> {
     ///
     /// A policy allowing propagation is insecure and should only be available for test code.
     cross_origin_credential_policy: CrossOriginCredentialsPolicy,
+    /// Optional custom reqwest client to use instead of creating a new one.
+    custom_client: Option<Client>,
 }
 
 /// The policy for handling HTTP redirects.
@@ -143,11 +145,23 @@ impl BaseClientBuilder<'_> {
             proxies: vec![],
             redirect_policy: RedirectPolicy::default(),
             cross_origin_credential_policy: CrossOriginCredentialsPolicy::Secure,
+            custom_client: None,
         }
     }
 }
 
 impl<'a> BaseClientBuilder<'a> {
+    /// Use a custom reqwest client instead of creating a new one.
+    ///
+    /// This allows you to provide your own reqwest client with custom configuration.
+    /// Note that some configuration options from this builder will still be applied
+    /// to the client via middleware.
+    #[must_use]
+    pub fn with_custom_client(mut self, client: Client) -> Self {
+        self.custom_client = Some(client);
+        self
+    }
+
     #[must_use]
     pub fn keyring(mut self, keyring_type: KeyringProviderType) -> Self {
         self.keyring = keyring_type;
@@ -267,29 +281,6 @@ impl<'a> BaseClientBuilder<'a> {
     }
 
     pub fn build(&self) -> BaseClient {
-        // Create user agent.
-        let mut user_agent_string = format!("uv/{}", version());
-
-        // Add linehaul metadata.
-        if let Some(markers) = self.markers {
-            let linehaul = LineHaul::new(markers, self.platform);
-            if let Ok(output) = serde_json::to_string(&linehaul) {
-                let _ = write!(user_agent_string, " {output}");
-            }
-        }
-
-        // Check for the presence of an `SSL_CERT_FILE`.
-        let ssl_cert_file_exists = env::var_os(EnvVars::SSL_CERT_FILE).is_some_and(|path| {
-            let path_exists = Path::new(&path).exists();
-            if !path_exists {
-                warn_user_once!(
-                    "Ignoring invalid `SSL_CERT_FILE`. File does not exist: {}.",
-                    path.simplified_display().cyan()
-                );
-            }
-            path_exists
-        });
-
         // Timeout options, matching https://doc.rust-lang.org/nightly/cargo/reference/config.html#httptimeout
         // `UV_REQUEST_TIMEOUT` is provided for backwards compatibility with v0.1.6
         let timeout = env::var(EnvVars::UV_HTTP_TIMEOUT)
@@ -307,23 +298,11 @@ impl<'a> BaseClientBuilder<'a> {
             .unwrap_or(self.default_timeout);
         debug!("Using request timeout of {}s", timeout.as_secs());
 
-        // Create a secure client that validates certificates.
-        let raw_client = self.create_client(
-            &user_agent_string,
-            timeout,
-            ssl_cert_file_exists,
-            Security::Secure,
-            self.redirect_policy,
-        );
-
-        // Create an insecure client that accepts invalid certificates.
-        let raw_dangerous_client = self.create_client(
-            &user_agent_string,
-            timeout,
-            ssl_cert_file_exists,
-            Security::Insecure,
-            self.redirect_policy,
-        );
+        // Use the custom client if provided, otherwise create a new one
+        let (raw_client, raw_dangerous_client) = match &self.custom_client {
+            Some(client) => (client.clone(), client.clone()),
+            None => self.create_secure_and_insecure_clients(timeout),
+        };
 
         // Wrap in any relevant middleware and handle connectivity.
         let client = RedirectClientWithMiddleware {
@@ -375,6 +354,51 @@ impl<'a> BaseClientBuilder<'a> {
         }
     }
 
+    fn create_secure_and_insecure_clients(&self, timeout: Duration) -> (Client, Client) {
+        // Create user agent.
+        let mut user_agent_string = format!("uv/{}", version());
+
+        // Add linehaul metadata.
+        if let Some(markers) = self.markers {
+            let linehaul = LineHaul::new(markers, self.platform);
+            if let Ok(output) = serde_json::to_string(&linehaul) {
+                let _ = write!(user_agent_string, " {output}");
+            }
+        }
+
+        // Check for the presence of an `SSL_CERT_FILE`.
+        let ssl_cert_file_exists = env::var_os(EnvVars::SSL_CERT_FILE).is_some_and(|path| {
+            let path_exists = Path::new(&path).exists();
+            if !path_exists {
+                warn_user_once!(
+                    "Ignoring invalid `SSL_CERT_FILE`. File does not exist: {}.",
+                    path.simplified_display().cyan()
+                );
+            }
+            path_exists
+        });
+
+        // Create a secure client that validates certificates.
+        let raw_client = self.create_client(
+            &user_agent_string,
+            timeout,
+            ssl_cert_file_exists,
+            Security::Secure,
+            self.redirect_policy,
+        );
+
+        // Create an insecure client that accepts invalid certificates.
+        let raw_dangerous_client = self.create_client(
+            &user_agent_string,
+            timeout,
+            ssl_cert_file_exists,
+            Security::Insecure,
+            self.redirect_policy,
+        );
+
+        (raw_client, raw_dangerous_client)
+    }
+
     fn create_client(
         &self,
         user_agent: &str,
diff --git a/crates/uv-client/src/registry_client.rs b/crates/uv-client/src/registry_client.rs
index a1a7b22fa..c2a8373ce 100644
--- a/crates/uv-client/src/registry_client.rs
+++ b/crates/uv-client/src/registry_client.rs
@@ -68,6 +68,12 @@ impl RegistryClientBuilder<'_> {
 }
 
 impl<'a> RegistryClientBuilder<'a> {
+    #[must_use]
+    pub fn with_reqwest_client(mut self, client: reqwest::Client) -> Self {
+        self.base_client_builder = self.base_client_builder.with_custom_client(client);
+        self
+    }
+
     #[must_use]
     pub fn index_locations(mut self, index_locations: &IndexLocations) -> Self {
         self.index_urls = index_locations.index_urls();