Alexander attended John Shaw High School, before moving on to Florida A&M University. He became a starter at wide receiver as a sophomore, posting 38 receptions for 535 yards and one touchdown. The next year, he registered 41 receptions for 941 yards and 10 touchdowns. He was a dominant player as a senior, earning MEAC offensive player of the year honors, while tallying 57 receptions for 1,079 yards and 9 touchdowns. Alexander finished his college career with school records for career receptions, career receiving yards, career touchdown receptions, career 100-yard receiving games, single-season receiving yards, single-season receptions, single-game receptions, single-game receiving yards and single-game receiving touchdowns. In 1995, he was inducted into the Mid-Eastern Athletic ConferenceHall of Fame.
In 1986, he signed with the Calgary Stampeders of the Canadian Football League. He was named a starter at wide receiver, registering 88 catches for 1,590 yards and 10 touchdowns, while receiving West All-Star honors.
Dallas Cowboys
On March 23, 1987, the Dallas Cowboys signed him as a free agent, hoping that his success in Canada could translate into the NationalFootball League. He suffered a broken left wrist during training camp and was placed on the injured reserve list. The next year, the team lost promising wide receiver Mike Sherrard to injury for a second year in a row and Alexander became a starter in a young receivers corps, that included rookie Michael Irvin. He led the team with 54 catches for 788 yards and 6 touchdowns. Almost a third of his 54 receptions were a first down or a touchdown on third or fourth down situations. He had a career-high 112 yards on 8 receptions against the Philadelphia Eagles. He was released on September 1, 1989, and later re-signed on September 18 to play in two games.
On March 13, 1990, he returned for a second stint in the Canadian Football League, signing as a free agent with the BC Lions. In his first season back, he recorded 65 receptions for 1,120 yards and his second West All-Star award. In 1991, he had a career-year with 104 catches for 1,650 yards and received both West and CFL All-Star honors. He was released in June 1992, only to be re-signed in August, finishing with 10 games and 56 receptions for 786 yards. In 1993, he returned to form with 77 receptions for 1,300 yards and 4 touchdowns. The next year, he recorded 85 catches for 1,234 yards and 6 touchdowns, receiving his last West All-Star nod.
In 1995, he was signed as a free agent by the Ottawa Rough Riders, posting 59 receptions for 801 yards and 5 touchdowns in 14 games. On March 13, 1996, he was traded back to the BC Lions in exchange for wide receiver Robert Gordon, but never played another game.