Martin was born Dino Paul Crocetti in Steubenville, Ohio, to Gaetano Alfonso "Guy" Crocetti, an Italian immigrant and barber, and his Ohio-born wife, Angela (Barra) Crocetti. He spoke only Italian until age five. Martin came up the hard way, with such jobs as a boxer ("Kid Crochet"), a steel mill worker, a gas station worker and a casino croupier/dealer. In 1946, Martin got his first ticket to stardom, as he teamed up with another hard worker who was also trying to succeed in Hollywood: Jerry Lewis. Films such as At War with the Army (1950) sent the team toward super-stardom. The duo were to become one of Hollywood's truly great teams. They lasted 11 years together, and starred in 16 movies. They were unstoppable, but personality conflicts broke up the team. Even without Lewis, Martin was a true superstar.

Few thought that Martin would go on to achieve solo success, but he did, winning critical acclaim for his role in The Young Lions (1958) with Marlon Brando and Montgomery Clift, and Some Came Running (1958), with Shirley MacLaine and Frank Sinatra. Movies such as Rio Bravo (1959) brought him international fame. One of his best remembered films is in Ocean's Eleven (1960), in which he played Sam Harmon alongside the other members of the legendary Rat Pack: Frank Sinatra, Sammy Davis Jr., Joey Bishop and Peter Lawford. Martin proved potent at the box office through the 1960s, with films such as Bells Are Ringing (1960) and Robin and the 7 Hoods (1964), again with Rat Pack pals Sammy Davis Jr. and Sinatra. During much of the 1960s and 1970s, his film persona of a boozing playboy prompted a series of films as secret agent Matt Helm and his own television variety show. Airport (1970) followed, featuring Martin as a pilot. He played a phony priest in The Cannonball Run (1981).

In 1965, Martin explored a new method for entertaining his fans: Television. That year he hosted one of the most successful TV series in history: The Dean Martin Show (1965), which lasted until 1973. In 1965, it won a Golden Globe Award. In 1973, he renamed it "The Dean Martin Comedy Hour", and from 1974 to 1984 it was renamed again, this time "The Dean Martin Celebrity Roasts". It became one of the most successful TV series in history, skewering such greats as Bob Hope, Frank Sinatra, Lucille Ball, James Stewart, George Burns, Milton Berle, Don Rickles, Phyllis Diller, and Joe Namath.

His last public role was a return to the stage, for a cross-country concert tour with Davis and Sinatra. He spoke affectionately of his fellow Rat Packers. "The satisfaction that I get out of working with these two bums is that we have more laughs than the audience has", Martin said. After the 1980s, Martin took it easy until his son, Dean Paul Martin, was killed in a plane crash in March 1987.

Devastated by the loss, from which he never recovered, he walked out on a reunion tour with Sinatra and Davis. Martin spent his final years in solitude, out of the public light. A heavy smoker most of his life, Martin died on Christmas Day 1995 at age 78 from complications to lung cancer.