Davis attended Iowa State University, and played for the Iowa State Cyclones football team from 1993 to 1996. He set numerous Cyclone team records, including most career rushing yards (4,382), total rushing yards in a single season (2,185), rushing yards in a game (378, vs. Missouri, rushing attempts in a game (53, vs. then-Division I-AA Northern Iowa, most rushing touchdowns in a game (5, vs. UNLV and vs. Northern Iowa), most 100-yard rushing games in a season (11) and career (21), most 200-yard rushing games in a season (5) and career (9), and most consecutive 100-yard rushing games (17, during 1995 and 1996 seasons), and most consecutive games scoring a touchdown (10, during 1995 and 1996 seasons). He also holds the Iowa State Cyclones football record for most career rushing touchdowns (36) and is tied for first for most career total touchdowns (38). He became the first running back in NCAA Division I-A (now Football Bowl Subdivision) history to gain 2,000 yards in two different seasons. During his 3 seasons at ISU, the Cyclones finished last in the Big Eight standings in his sophomore and junior seasons and last in the Big 12 North division standings. Davis played for head coaches Jim Walden and for the final two years of his ISU career, Dan McCarney.
In 1996, Davis was selected as the Big 12 Conference Player of the Year. He was recognized as a consensus first-team All-American at running back in 1995 and 1996. He was inducted into the Iowa State Sports Hall of Fame in 2007.
Davis finished fifth out of six finalists for the Heisman Trophy in 1995. In 1996, he narrowly finished second to winner Danny Wuerffel. He won three out of four Heisman regions, but lost badly in the South region. He was nosed out for the 1996 Doak Walker Award by another Big 12 running back, Byron Hanspard of Texas Tech. In both cases, he was largely hampered by the fact that he played on a losing team.
Davis elected to forgo his senior season of eligibility and declared for the 1997 NFL Draft. He was drafted in the 3rd round (62nd overall) by the New Orleans Saints. He played in the NFL for three years before joining the Hamilton Tiger-Cats of the Canadian Football League. In 2004, he led the CFL with 1628 rushing yards. He also set the Tiger Cats record for both rushing yards with 1628 and yards from scrimmage with 1878. During the 2005 CFL season, Davis was traded to the Edmonton Eskimos in exchange for a package headlined by wide receiverBrock Ralph, defensive backTay Cody, and a first-round pick in that year's draft. Davis played a key role in helping the Eskimos win the 93rd Grey Cup that year. On February 23, 2007, the Eskimos released Davis. He was later signed to the Toronto Argonauts' practice roster on September 25, 2007. Davis was initially released by the Argonauts on October 17, 2007, but rejoined their practice roster on October 23, 2007.
Davis is the brother of Darren Davis, who played running back at Iowa State beginning in Troy's final season until 1999. Darren ran for over 1,000 yards in three consecutive seasons before ending his career second in career rushing yards behind his older brother.