Ensign was born in Safford, Arizona, and was raised in both the United States and England. He trained at the London Academy of Music and Dramatic Art and spent the first ten years of his professional career working in the theatre in Britain.
Born into a family in the Church of Jesus Christ of Latter Day Saints, he later became a member of the Episcopal Church, attending a parish which is in the Anglo-Catholic tradition.
He was a member of the Royal Shakespeare Company in the 1970s, appearing in productions of As You Like It, Love's Labour's Lost, and Cymbeline amongst others. He has appeared in Irene, Curse of the Starving Class, and The Red Devil Battery Sign in the West End.
Ensign's film credits include Superman (1978), Pink Floyd – The Wall (1982), WarGames (1983), Ghostbusters (1984), Dr. Hackenstein (1988), Titanic (1997, as Benjamin Guggenheim), Solaris (2002), and Seabiscuit (2003).
Ensign's many television appearances include Boston Legal, Alias, Monk, JAG, CSI: Crime Scene Investigation, Star Trek: Enterprise, The X Files, Friends, Star Trek: Voyager, Star Trek: Deep Space Nine, Star Trek: The Next Generation, MacGyver, Dynasty, Falcon Crest, M*A*S*H, The A-Team, and The Dukes Of Hazzard. He appeared in the TV miniseries The Winds of War and Dream West.
Ensign also voices Dr. Nefarious Tropy in most of the Crash Bandicoot games, with the exception of Crash Bandicoot: The Wrath of Cortex and Crash Bandicoot N. Sane Trilogy, in which Corey Burton voiced the character. He gave his voice for Dr. Sebastian Wolfe in 2011 video game inFamous 2. In 2009 Michael Ensign was given the Distinguished Alumnus Award for Theatre from the College of Fine Arts at University of Utah in Salt Lake City.
Writing in Forbes in 2011, David M. Ewalt noted,
"Ensign is a classic example of "Hey! It's that guy!" --a versatile character actor with a long and illustrious career, but who you probably can't identify by name, or even where you've seen him", before going on to list some of Ensign's key film appearances.
Michael is a member of the Academy of Motion Picture Arts and Sciences.