Born on June 21, 1955 in Los Angeles, California, Leigh McCloskey was classically trained as an actor at the Juilliard School in Lincoln Center, New York. He began his professional acting career playing Billy Abbott in the original miniseries Zengin ve Yoksul (1976) starring Nick Nolte and Peter Strauss. He went on to star in three nighttime television series: Executive Suite (1976), Married: The First Year (1979), and is perhaps most widely known for his role as Lucy Ewing's husband Mitch Cooper on the CBS nighttime soap opera Dallas (1978). McCloskey was a series regular from 1980-1982, and made brief appearances in 1985 and 1988. In 1978, he married production executive Carla Reinke, and they have two daughters: Caytlyn Alexander and Brighton Aubreigh.

McCloskey starred in numerous made-for-television films and miniseries including The Bermuda Depths (1978) with Connie Sellecca, Dawn: Portrait of a Teenage Runaway (1976) and its sequel Alexander: The Other Side of Dawn (1977) in which he played the title role. He starred with Kris Kristofferson in Trouble Shooters: Trapped Beneath the Earth (1993) and with his Dallas co-star Linda Gray in Accidental Meeting (1994). He also co-starred with Brooke Shields and Scott Glenn in the television miniseries Gone But Not Forgotten (2005). McCloskey has also had made numerous films including Acemi Aşık (1985) with Tim Robbins, Just One of the Guys (1985), Cameron's Closet (1988), and the cult classic Cehennem (1980) directed by Dario Argento among others.

McCloskey has guest-starred on numerous television series and pilots including Tıp Merkezi (1969), Jake and the Fatman (1987), Life Goes On (1989), Star Trek: Deep Space Nine (1993), Star Trek: Voyager (1995), Chicago Hope (1994), JAG (1995), Bones (2005) and many others. He has played villains on four sci-fi television series: Star Trek: Deep Space Nine (1993), Star Trek: Voyager (1995), Babylon 5 (1993) and 25. yüzyıl (1979) with Dorothy Stratten. He has also appeared in a number of daytime soap operas, including General Hospital (1963), One Life to Live (1968), Yalan Rüzgârı (1973) and Santa Barbara (1984).