Cosgrove was born in New Haven, Connecticut and grew up in Branford, Connecticut, but later moved to New York City to join the cast as "Scott Chandler" on the ABC soap opera All My Children in 1996. After two years with the soap, he left the show in the fall of 1998 to explore other opportunities. That same year, Cosgrove moved to Los Angeles to join the cast as "Matt Durning" on Beverly Hills 90210, where he remained until the show ended in 2000.
He played "Dick Bagg" in the 2002 comedy film Van Wilder. In June 2002, he moved back to New York to join the cast of Guiding Light as "Bill Lewis". He began on the CBS soap, Guiding Light on June 5 2002, and opted not to renew his contract in October 2005; his last day was October 18 2005. He later returned to the role in October 2007 and was nominated for his first Daytime Emmy for Outstanding Supporting Actor in a Drama Series in 2008.
Cosgrove moved back to California for his role as "Jon Lemonick" in the series, In Justice, which premiered on ABC in January 2006. In September 2007, he portrayed "Freddy Manson" on the ABC drama, Dirty Sexy Money.