diff --git a/CHANGELOG.md b/CHANGELOG.md
index 26312e3..d0c5f8a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+# 0.18.1 - unreleased
+
+- Add `with_p2p` on `Multiaddr`. See [PR 102].
+
+[PR 102]: https://github.com/multiformats/rust-multiaddr/pull/102
+
 # 0.18.0
 
 - Add `WebTransport` instance for `Multiaddr`. See [PR 70].
diff --git a/src/lib.rs b/src/lib.rs
index 92a31fb..999738b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -26,6 +26,8 @@ use std::{
     sync::Arc,
 };
 
+use libp2p_identity::PeerId;
+
 #[cfg(feature = "url")]
 pub use self::from_url::{from_url, from_url_lossy, FromUrlErr};
 
@@ -127,6 +129,18 @@ impl Multiaddr {
         self
     }
 
+    /// Appends the given [`PeerId`] if not yet present at the end of this multiaddress.
+    ///
+    /// Fails if this address ends in a _different_ [`PeerId`].
+    /// In that case, the original, unmodified address is returned.
+    pub fn with_p2p(self, peer: PeerId) -> std::result::Result<Self, Self> {
+        match self.iter().last() {
+            Some(Protocol::P2p(p)) if p == peer => Ok(self),
+            Some(Protocol::P2p(_)) => Err(self),
+            _ => Ok(self.with(Protocol::P2p(peer))),
+        }
+    }
+
     /// Returns the components of this multiaddress.
     ///
     /// # Example
diff --git a/tests/lib.rs b/tests/lib.rs
index 071a4ce..7c2d659 100644
--- a/tests/lib.rs
+++ b/tests/lib.rs
@@ -661,3 +661,66 @@ fn arbitrary_impl_for_all_proto_variants() {
     let variants = core::mem::variant_count::<Protocol>() as u8;
     assert_eq!(variants, Proto::IMPL_VARIANT_COUNT);
 }
+
+mod multiaddr_with_p2p {
+    use libp2p_identity::PeerId;
+    use multiaddr::Multiaddr;
+
+    fn test_multiaddr_with_p2p(
+        multiaddr: &str,
+        peer: &str,
+        expected: std::result::Result<&str, &str>,
+    ) {
+        let peer = peer.parse::<PeerId>().unwrap();
+        let expected = expected
+            .map(|a| a.parse::<Multiaddr>().unwrap())
+            .map_err(|a| a.parse::<Multiaddr>().unwrap());
+
+        let mut multiaddr = multiaddr.parse::<Multiaddr>().unwrap();
+        // Testing multiple time to validate idempotence.
+        for _ in 0..3 {
+            let result = multiaddr.with_p2p(peer);
+            assert_eq!(result, expected);
+            multiaddr = result.unwrap_or_else(|addr| addr);
+        }
+    }
+
+    #[test]
+    fn empty_multiaddr() {
+        // Multiaddr is empty -> it should push and return Ok.
+        test_multiaddr_with_p2p(
+            "",
+            "QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN",
+            Ok("/p2p/QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN"),
+        )
+    }
+    #[test]
+    fn non_p2p_terminated() {
+        // Last protocol is not p2p -> it should push and return Ok.
+        test_multiaddr_with_p2p(
+            "/ip4/127.0.0.1",
+            "QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN",
+            Ok("/ip4/127.0.0.1/p2p/QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN"),
+        )
+    }
+
+    #[test]
+    fn p2p_terminated_same_peer() {
+        // Last protocol is p2p and the contained peer matches the provided one -> it should do nothing and return Ok.
+        test_multiaddr_with_p2p(
+            "/ip4/127.0.0.1/p2p/QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN",
+            "QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN",
+            Ok("/ip4/127.0.0.1/p2p/QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN"),
+        )
+    }
+
+    #[test]
+    fn p2p_terminated_different_peer() {
+        // Last protocol is p2p but the contained peer does not match the provided one -> it should do nothing and return Err.
+        test_multiaddr_with_p2p(
+            "/ip4/127.0.0.1/p2p/QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN",
+            "QmcgpsyWgH8Y8ajJz1Cu72KnS5uo2Aa2LpzU7kinSupNKC",
+            Err("/ip4/127.0.0.1/p2p/QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN"),
+        )
+    }
+}