Rising to fame with his role as the alien Mork in the TV series Mork and Mindy, and later stand-up comedy work, Williams has performed in many feature films since 1980. He won the Academy Award for Best Supporting Actor for his performance in the 1997 film Good Will Hunting. He has also won two Emmy Awards, four Golden Globes, two Screen Actors Guild Awards and five Grammy Awards.

Williams was born in Chicago, Illinois. His mother, Laura (née Smith, 1922–2001), was a former model from New Orleans, Louisiana. His father, Robert Fitzgerald Williams (September 10, 1906 – October 18, 1987) was a senior executive at Ford Motorship in charge of the Midwest area. He is of English, Welsh and Irish descent on his father's side, and of French descent on his mother's side. Williams was raised in the Episcopal Church, though his mother practiced Christian Science. He grew up in Bloomfield Hills, Michigan, where he was a student at the Detroit Country Day School, and Marin County, California, where he attended the public Redwood High School. Williams also attended Claremont McKenna College (then called Claremont Men's College) for four years.[citation needed] He has two half-brothers: Todd (who died August 14, 2007) and McLaurin.

Williams has described himself as a quiet child whose first imitation was of his grandmother to his mother. He did not overcome his shyness until he became involved with his high-school drama department.

In 1973, Williams was one of only 20 students accepted into the freshman class at the Juilliard School, and one of only two students to be accepted by John Houseman into the Advanced Program at the school that year, the other being Christopher Reeve. In his dialects class, Williams had no trouble mastering all dialects quickly. Williams left Juilliard in 1976.

After appearing in the cast of the short-lived The Richard Pryor Show on NBC, Williams was cast by Garry Marshall as the alien Mork in the hit TV series "Happy Days". As Mork, Williams improvised much of his dialogue and devised plenty of rapid-fire verbal and physical comedy, speaking in a high, nasal voice. Mork's appearance was so popular with viewers that it led to a spin-off hit television sitcom, Mork and Mindy, which ran from 1978 to 1982. Although playing the same character as in his appearance in Happy Days, the show was set in the present day, in Boulder, Colorado, instead of the late '50s in Milwaukee. Mork was an extremely popular character, featured on posters, coloring books, lunchboxes, and other merchandise.

Starting in the late 1970s and throughout the 1980s, Williams began to reach a wider audience with his standup comedy, including three HBO comedy specials, Off The Wall (1978), An Evening with Robin Williams (1982), and Robin Williams: Live at the Met (1986). Also in 1986, Williams reached an ever wider audience to exhibit his style at the 58th Academy Awards show; noting the Hollywood writers' strike that year he commented that the Hollywood writer... "is the only man in the world that can blow smoke up his own ass." As a result, Williams has never hosted the Academy Awards again.[citation needed]

His stand-up work has been a consistent thread through his career, as is seen by the success of his one-man show (and subsequent DVD) Robin Williams Live on Broadway (2002). He was voted 13th on Comedy Central's list "100 Greatest Stand-ups of All Time" in 2004.

After some encouragement from his friend Whoopi Goldberg, he was set to make a guest appearance in the 1991 Star Trek: The Next Generation episode, "A Matter of Time", but he had to cancel due to a scheduling conflict; Matt Frewer took his place as a time-traveling con man, Professor Berlingoff Rasmussen.

Williams also appeared on an episode of the American version of Whose Line Is It Anyway? (Season 3, Episode 9: November 16, 2000). During a game of "Scenes from a Hat", the scene "What Robin Williams is thinking right now" was drawn, and Williams stated "I have a career. What the hell am I doing here?"

Most of Williams' acting career has been in film, although he has given some performances on stage as well (notably as Estragon in a production of Waiting for Godot with Steve Martin). His performance in Good Morning, Vietnam (1987) got Williams nominated for an Academy Award. Many of his roles have been comedies tinged with pathos.