He played primarily as a catcher and attracted little attention from college recruiters due to his mediocre offense.

He split time between the Kannapolis Intimidators and Winston-Salem Warthogs, saving 22 total games and striking out 83 batters in 751⁄3 innings of work.

He spent that entire season with the Birmingham Barons, making 55 relief appearances, posting a 4–1 record with a 1.97 ERA and saving 36 games.

Following his outstanding 2002 season, Valentine was involved in a major trade that sent Keith Foulke, Mark Johnson, cash and himself to the Oakland Athletics for players to be named later and Billy Koch.

Pitching for the Sacramento River Cats, Valentine slumped to a 1–3 record and 4.82 ERA, and was traded to the Cincinnati Reds with minor leaguer Jeff Bruksch and Aaron Harang for José Guillén.

Facing the Houston Astros on August 24, Valentine appeared in his first big league game, allowing one run in one inning of work.

He made 24 appearances for the Reds that year, making one start (which he lost) and posting a 2–3 record with a 4.22 ERA.

Signed by the Houston Astros, Valentine made 20 appearances with their Triple-A affiliate, the Round Rock Express.

Valentine started the 2008 season with the Ducks, making 14 appearances with them, saving six games and posting a 2–1 record and 1.62 ERA.

After his release in June, Valentine re-signed with the Ducks, but on August 4 his contract was purchased by the Cincinnati Reds, where he was assigned to Double-A Chattanooga.