Michael George Westmore is a scion of the Westmores of Hollywood, the most illustrious family of make-up artists in the business. The dynasty (of which Michael is the 13th to pursue this line of work) began with his grandfather George Westmore in 1917, later to become head of MGM's make-up department. Michael's father, Monte Westmore, headed the make-up department at Selznick International Pictures and worked on Gone with the Wind (1939) and Rebecca (1940) before his untimely death at the age of 37. His uncles included Bud Westmore, who worked at Universal and was one of the creators of the molded foam rubber suit used for the Creature from the Black Lagoon (1954); Wally Westmore, who headed the make-up department at Paramount; Ern Westmore, who occupied the same position at RKO; and Perc Westmore, chief make-up artist at Warner Brothers, who was responsible for Bette Davis's look as Queen Elizabeth I and for that of Paul Muni as Louis Pasteur, Emile Zola and Benito Juarez. Their collective contribution to the industry earned the Westmores a star on the Hollywood Walk of Fame on Vine Street.

A graduate of the University of California-Santa Barbara, Michael started at Universal in 1961. After three years, he rose to the position of Assistant Department Head of Make-Up. Turning free-lance in the 70s, he worked on the cult horror film Trilogy of Terror (1975), followed by Rocky (1976) (and three of the sequels) and Capricorn One (1977). For the biopic Raging Bull (1980), he transformed Robert De Niro into Jake LaMotta. His particular forte was to make actors age in the course of a film, which he did especially well in The Amazing Howard Hughes (1977) (Tommy Lee Jones) and in True Confessions (1981) (De Niro and Robert Duvall). He also excelled in the design and production of prosthetics, latex masks and the creation of special visual effects.

In 1986, Michael joined the Star Trek franchise as make-up supervisor and stayed on for eighteen years. Beginning with Star Trek: The Next Generation (1987), he devised the look for the characters Data and Lal, as well as creating prosthetics and make-up to bring the Ferengi, the Cardassians and the Borg to life (the Borg Queen was possibly his pièce de résistance!). He also redesigned the Klingons by giving them more pronounced forehead ridges (based on dinosaur spinal columns), nose ridges and dentures to simulate sharp, fang-like teeth. Michael explained: "I read the script and create. The script doesn't usually say three eyes, two horns and blowing fire, so I get to devise creations of my own imagination". His designs for Star Trek: Deep Space Nine (1993) include the featureless visage of the changeling Odo and the ferocious, bony features of the Nausicaans and the Jem'Hadar. His alien head designs for Star Trek: Voyager (1995) have included the reptilian Voth and for Star Trek: Enterprise (2001) the Xindi.

Michael based most of his creations on earth animals. For example, he saw the Jem'Hadar as a combination of dinosaurs and rhinos: "If you look at all the pieces, you can see the rhinoceros between the hairdo and the dinosaur with the top of the head and everything. So I would use combinations of what people are familiar with to create my aliens."

In the course of his four decade-long career, Michael has won nine Primetime Emmy Awards and an Oscar for his work on the film Mask (1985). In conjunction with special effects make-up artist Thomas R. Burman, he has also created make-up sets for the CIA for use by overseas agents in need of changing their identities. In 1973, he published a reference book, The Art of Theatrical Makeup for Stage and Screen, followed in 2017 by Makeup Man: From Rocky to Star Trek: The Amazing Creations of Hollywood's Michael Westmore.