Hilliard played college football for the Florida Gators, earning consensus All-American honors in 1996.

As a junior in 1996, he was paired with fellow Gators receiver Reidel Anthony and both posted 1,000-yard seasons, and both Hilliard and Anthony were recognized as first-team All-Southeastern Conference selections and consensus first-team All-Americans,[4][5] as the Gators won the Bowl Alliance national championship—their first-ever national football title.

The Gators finished the season with a record of 12–1 after a 52–20 victory over the top-ranked Florida State Seminoles in the 1997 Sugar Bowl.

It was the second of a Sugar Bowl-record three touchdowns for Hilliard and it gave the Gators a 24–10 advantage in what ended as a 52–20 Florida victory.

Hilliard's signature game against Georgia came in 1995 when he hauled in five passes for 99 yards and two touchdowns, as the Gators claimed a 52–17 victory over the Bulldogs.

[20] He became a regular starter in 1998,[20] and helped the Giants shut out the Minnesota Vikings 41–0 in the 2000 season NFC Championship Game.

As New York's wide receiver, he made 10 receptions for 155 yards and two touchdowns to help his team reach Super Bowl XXXV following the 2000 regular season.

During the second game of his rookie year, Hilliard was hit by Jacksonville safety Chris Hudson and sustained a sprained interspinous ligament between his sixth and seventh vertebrae.

[27] During his first two seasons with Tampa Bay, he was used mainly as a third or fourth receiver, but in 2007, he started ten games, in which he made sixty-two receptions for 722 yards.

[28] On October 19, 2008, Hilliard refused to be carted off the field during a Sunday Night Football 20–10 win over the Seattle Seahawks.

[30] He was one of five veterans that the Bucs released that day, the other four being wide receiver Joey Galloway, running back Warrick Dunn and linebackers Derrick Brooks and Cato June.

[31] In his twelve-season NFL career, Hilliard appeared in 161 regular-season games, starting in 105, and made 546 catches for 6,397 yards and thirty-five touchdowns.

The Redskins ended the regular season with a 7-game winning streak to finish with a 10–6 record, leading to a NFC East division championship and a fourth-seed spot in the playoffs.

[35] Hilliard oversaw a young group of receivers that included veteran Steve Johnson and rookies Robert Woods and Marquise Goodwin.

In January 2014, Hilliard was hired by Jay Gruden as the wide receivers coach of the Washington Redskins.

In his second stint with the Redskins, Hilliard led a veteran unit that included Pierre Garçon, DeSean Jackson and Santana Moss.

[36] During the 2019 season, Hilliard helped to develop a group of rookie receivers that included Terry McLaurin, Kelvin Harmon and Steven Sims.