Seay played wide receiver in football and center fielder in baseball at Compton, but transferred in 1981 to San Bernardino High School after his family decided to move. He would end up breaking many of the school's football offensive records, while helping lead the team to the playoff quarterfinals in his senior season.
Seay accepted a football scholarship at Cal State Long Beach in 1988. That year while attending his sister's children Halloween party, shots were fired outside the home, compelling him to shield his 2-year-old niece with his body. He resulted injured with a.38-caliber bullet that pierced through his pelvis, kidney and lung, stopping near his heart. He was hospitalized for 2 1/2 weeks, lost a kidney and spent two months eating only soup, while keeping strict bed rest. In 1989, he rejoined the football team, but school officials deemed him medically ineligible to avoid legal liability, in the event of the bullet close to his heart be dislodged or risking his remaining kidney to be damaged by a hit. He sued the university, but before the case went to court, former NFL great George Allen, who had just been named the new Cal State Long Beach head coach, helped him return to the team. As part of the compromise he dropped his lawsuit, signed a waiver absolving the university from liability, wore additional protective equipment and took urine tests after each game. As a junior and senior, he earned second-team All-Big West honors at wide receiver, with Allen going on record saying: "He's an example for all of us, what I call a solid citizen. He's a leader. One of the highlights of my coaching career is having a guy like Mark Seay on my team".
In 1992 with Bruce Allen as his agent, he was signed as an undrafted free agent by the San Francisco 49ers, after accepting a similar liability waiver as he did in college. He would make the team's practice squad, before being released in 1993 at the end of training camp.
San Diego Chargers
In 1993 the San Diego Chargers claimed him off waivers and kept him inactive for all but one regular season game. In 1994 he became a favorite target of quarterbackStan Humphries as a slot receiver, tying the team lead in receptions with Ronnie Harmon and helping the Chargers reach Super Bowl XXIX against the San Francisco 49ers, after catching a game-winning touchdown pass in a playoff game against the Miami Dolphins. In Super Bowl XXIX, Seay was on the receiving end of the first successful two-point conversion in Super Bowl history, via a Stan Humphries pass.
Philadelphia Eagles
In 1996 he signed as a free agent with the Philadelphia Eagles where he played wide receiver and special teams. He retired at the end of the 1997 season, with 135 receptions for 1,629 yards and 10 touchdowns.
Personal life
His father Elvin Seay Sr. died from a stroke when he was 14. In 2003 His older brother Elvin Seay Jr., 41, was shot in a San Bernardino motel parking lot and spent 11 months in a coma before passing away. In 2006 his younger brother James Seay, 37, was shot to death in the family's backyard by two assailants. In 2008, he graduated from the SBVC Extended Basic Police Academy. Seay is also a motivational speaker.
