He served as the head football coach at Hofstra University for 16 seasons, from 1990 to 2005, compiling a record of 119–62–2.

[2] In 1964, he was hired as the head football coach for the Oratory Preparatory School in Summit, New Jersey.

[2] In 1970, Gardi returned to his alma mater to assume the roles of assistant head coach for the freshman team and recruiting coordinator.

That year, he was responsible for recruiting future star quarterback, Bob Avellini.

In 1975, he served as head coach for the Portland Thunder for three games before the league disbanded.

In his first year running the defense, the Jets allowed 304 yards per game, a conference best, and posted 66 sacks, the highest in the NFL.

The following season, the Jets participated in the AFC Championship Game, where they lost to the Miami Dolphins.

In 1995, Hofstra lost in the first round of the playoffs to finish with a 10–2 record and a number-ten national ranking.

[1] Gardi was inducted into the Suffolk Sports Hall of Fame on Long Island in the Football and Coaches Categories with the Class of 2000.

[5] During his coaching career, he had helped develop future NFL players such as Wayne Chrebet, Lance Schulters, Marques Colston, Willie Colon, and Raheem Morris.