In 1978, he was cast as an extra of a dancing role in the musical adaptation film Grease starring actor John Travolta and singer/actress Olivia Newton-John.

He was cast as Boy Greaser in the sequel musical romantic-comedy Grease 2 starring actor Maxwell Caulfield and actress Michelle Pfeiffer in 1982.

Tennant quit acting and began writing and producing with his first project being the NBC made-for-television movie Moving Target in 1988 starring actor/comedian Jason Bateman, singer/actress Chynna Phillips and actor Jack Wagner.

He worked as a director and producer for two episodes of the NBC adaptation of the 1980s John Hughes film Ferris Bueller starring actor Charlie Schlatter in 1990.

He directed four episodes from season 1 of the Fox sitcom Parker Lewis Can't Lose starring actor Corin Nemac (1990).

He directed the made-for-television movie Desperate Choices: To Save My Child starring actress Joanna Kerns and actor Bruce Davison in 1992.

He directed two episodes of the Fox weird western series The Adventures of Brisco County, Jr. starring actor Bruce Campbell in 1993.

He returned to television to directed as well as co-produce an episode of the Fox drama series The American Embassy starring actress Arija Bareikis in 2002.

He directed the made-for-television Fox movie The Wedding Album starring actor Bruno Campos and actress Tara Summers in 2006.