Deaver was born in Bakersfield, California, the son of Marian (née Mack) and Paul Sperling Deaver, a Shell Oil Co. distributor. He graduated from Desert High School at North Edwards, California in 1956. He received his bachelor's degree in political science from San Jose State College (now San Jose State University). Deaver was initiated and a member of the Delta Sigma Phi fraternity at San José State.
He worked for IBM, served in the United States Air Force, and later was executive director of the Santa Clara County Republican Party. While Ronald Reagan was running for governor of California, Deaver worked as a political field representative for the California Republican Party, running several state assembly campaigns. After being elected governor, Reagan's chief of staff recruited Deaver to the administration where he began a 30-year career working for Reagan, and building a very close friendship with him and Nancy Reagan.
Deaver formed his own consulting company after Reagan's term as governor, where Reagan and his upcoming presidential campaigns were among his clients. Accompanying Reagan on his campaign plane in 1976, Deaver performed the Heimlich maneuver on the candidate in order to dislodge a peanut stuck in his throat and reportedly saved the future President's life. Though initially he disliked the idea of moving to Washington, D.C., he ultimately agreed and was appointed Deputy Chief of Staff under President Reagan in 1981. He principally had responsibility for the president's schedule of events and speeches, and public relations.
While serving on Reagan's staff, Deaver worked closely with Chief of Staff James Baker and Counsellor to the President Ed Meese. They were known as "The Troika" by some observers of the White House due to their influence over policy while they served on the White House staff.
As Deputy Chief of Staff at the White House, Deaver worked primarily on media management forming how the public perceived Reagan, sometimes by engineering press events so that the White House set the networks' agenda for covering the president.
Deaver once saved Reagan using the Heimlich maneuver. Deaver resigned from the White House staff in May 1985.
On March 18, 1987, Deaver was convicted of perjury for congressional testimony he had submitted. He was convicted on three of five counts of perjury stemming from statements to a congressional subcommittee and federal grand jury investigating his lobbying activities with administration officials. Deaver blamed alcoholism for lapses in memory and judgment. He was sentenced to three years' in prison, but the sentence was reduced to three years of probation and a fine of $100,000. Deaver was also ordered to perform 1,500 hours of public service. In the final days of Reagan's presidency the question of a pardon arose, but Reagan noted in his diaries that Deaver indicated he would not accept a pardon.
Shortly after Deaver resigned from the White House, he formed Michael K. Deaver, Inc. and became a lobbyist. For a time he was in business with another Reagan aide, Peter D. Hannaford in a public relations firm named Deaver and Hannaford.
In his later years, he wrote three books: Behind the Scenes (1988; co-written with Mickey Herskowitz), A Different Drummer: My Thirty Years with Ronald Reagan (2001; foreword by Nancy Reagan), and Nancy: A Portrait of My Years with Nancy Reagan (2004). In 2005, he edited and published a collection of essays titled Why I Am a Reagan Conservative.
Deaver also worked at the Washington, D.C. office of Edelman, a public relations agency, a role he held from 1992–2006, ultimately as chairman of the D.C. office. In an interview with the Los Angeles Times in 2001, Deaver said, "I've always said the only thing I did is light [Reagan] well... My job was filling up the space around the head. I didn't make Ronald Reagan. Ronald Reagan made me." According to former first lady and longtime friend Nancy Reagan, Deaver's greatest skill "was in arranging what were known as good visuals — televised events or scenes that would leave a powerful symbolic image in people's minds." In 2006, Deaver was awarded an honorary degree from Universidad Francisco Marroquin in Guatemala City, Guatemala.
Deaver died of pancreatic cancer on August 18, 2007 at age 69 at his home in Maryland. He is survived by his wife, Carolyn, and their two children, Amanda Deaver of Washington and Blair Deaver of Bend, Oregon. In a statement, Nancy Reagan, who attended the funeral of former talk show host Merv Griffin only the day before, said on the 18th, "[Deaver] was the closest of friends to both Ronnie and me in many ways, and he was like a son to Ronnie... We met great challenges together... I will miss Mike terribly."