Tim Horner grew up in Roanoke, Virginia, the son of musical parents. He started on drums at age ten after an earlier introduction to music through church choir singing and public-school string instruction on violin and viola, and he played in the Roanoke Civic Orchestra as a teenager. He enrolled at Berklee College of Music in Boston in 1974, studying percussion under Dean Anderson and Keith Copeland and taking additional instruction from bassist Miroslav Vitous, and completed a bachelor's degree in performance in 1979 while already working professionally. His first major road job came in 1978 with a touring edition of the Tommy Dorsey Orchestra. After six years based in Boston, Horner relocated to Brooklyn in 1980 and quickly established himself among New York's in-demand jazz drummers, appearing at the Village Vanguard, Birdland, the Blue Note, and Lincoln Center.

His own quintet, featuring vibraphonist Joe Locke and bassist Ed Howard, won the 1985 Hennessy Jazz Search, an early marker of his standing as a bandleader as well as a sideman. Through the late 1980s and 1990s his sideman work built steadily: a full-album drum credit on singer Carla White's Orient Express (1987, Milestone), pianist Bill Mays's Mays In Manhattan (1996, Concord Jazz) alongside trumpeter Marvin Stamm, bassist Ben Allison's Seven Arrows (1996, Koch Records), and Coming About (1996, Enja Records), one of several dates with the Maria Schneider Jazz Orchestra. The same year he recorded Inner Space (SteepleChase) with the Joe Locke Quartet alongside bassist Harvie Swartz, a pairing that would recur more than two decades later. He also joined guitarists Charlie Byrd, Herb Ellis, and Mundell Lowe, with special guest Larry Coryell, on The Return of the Great Guitars (1996, Concord Jazz), and drummed on the Jazz Composers Collective's Herbie Nichols tribute, Dr. Cyclops' Dream (1999, Soul Note), with Ben Allison, Frank Kimbrough, Ted Nash, and Michael Blake.

Horner's own leader catalog began with the collectively billed quartet album Cotangent (2002, Sable Records/Art of Life Records) with pianist Bill Gerhardt, saxophonist Marc Mommaas, and bassist François Moutin, and he later recorded two further albums under the same group name. His first true solo leader date, The Places We Feel Free (2011, Miles High Records), gathered bassist Martin Wind, guitarist John Hart, pianist Jim Ridl, saxophonists Scott Robinson and Marc Mommaas, trumpeter Ron Horton, and vibraphonist Mark Sherman around his own compositions; he followed it with The Head of the Circle (2013, Origin Records), featuring Ted Nash, Joe Locke, Jim Ridl, Steve Allee, and Dean Johnson. In between and since, he has recorded as an equal co-leader rather than a sole leader more often than not: Good Rhythm / Good Vibes (2010, Miles High Records) with the Mark Sherman & Tim Horner Quartet, Border Widow's Lament (2023, Night Is Alive Records) as one-third of a trio with pianist Bill Cunliffe and bassist Martin Wind, and August 17th Vol. 4 (2022, Pepjack Records), a standards-and-bebop trio session with saxophonist Michael Morreale and bassist Bill Moring. In 2025 he released Moving Forward (ABTH Records) as a co-billed project with guitarist Allan Bezama, with a release-show band that added Steve Wilson, Jim Ridl, and Noriko Ueda.

Across four decades Horner's sideman catalog runs past 250 recordings, including repeat associations with guitarists Dave Stryker and Vic Juris on SteepleChase Records, vibraphonist Mark Sherman, singer Roseanna Vitro (with whom he also traveled as a State Department Jazz Ambassador), singer Sarah Partridge, bassist Rufus Reid's quintet, bassist Martin Wind's own quartet, and a run of Venus Records dates backing singer/bassist Nicki Parrott. In 2018 he drummed on Introspection (Jazzheads), the duo-billed but trio-recorded album by guitarist Roni Ben-Hur and bassist Harvie S, joining Harvie S in the studio for the second time since their 1996 session together in the Joe Locke Quartet. Since 2000 Horner has served five times as a Jazz Ambassador for the U.S. State Department, performing and teaching in more than twenty countries, and he has taught jazz drumset for many years on the faculty of New Jersey City University as well as at the New York Jazz Workshop.

Horner is a mainstream, post-bop drummer whose reputation rests on time-feel and taste rather than flash: his own teaching material stresses "steady, consistent time" and a deep pocket groove, with accompaniment skills as the foundation a soloist's vocabulary is built on. That approach has made him a first-call sideman across a wide range of settings, from big-band chairs with the Village Vanguard Jazz Orchestra and the Maria Schneider Jazz Orchestra to small-group work behind singers (Roseanna Vitro, Sarah Partridge, Nicki Parrott), guitarists (Dave Stryker, Vic Juris, John Hart, Roni Ben-Hur), and vibraphonists (Joe Locke, Mark Sherman). His own compositions, heard on The Places We Feel Free and The Head of the Circle, favor lyrical, harmonically open writing suited to the mixed horn-and-vibraphone frontlines he consistently assembles as a leader.