Rocco was born as Alexander Federico Petricone in Cambridge, Massachusetts in 1936, but raised in nearby Somerville, the son of Mary (née DiBiase; October 1909–August 1978) and Alessandro Sam Petricone. He was of Italian descent.  According to organized crime turncoat Vincent Teresa, Alex was a hanger-on with the Winter Hill Gang of the Boston area. An unwanted advance toward Petricone’s then girlfriend on Labor Day, 1961, touched off the Boston Irish Gang War of the 1960s. Georgie McLaughlin who made the advance was beaten by Winter Hill Gang members. Howie Carr, a Boston-area journalist and radio personality who has written extensively about the Boston underworld, has written that the young Petricone (whose nickname was “Bobo”) was arrested in Charlestown in November 1961 along with Winter Hill boss Buddy McLean for questioning following the death of Bernie McLaughlin of the McLaughlin gang, the first murder of the war. Petricone was released without charge, and shortly thereafter left the Boston area. (When he returned to the Boston area in 1972 to play a bank robber in the film The Friends of Eddie Coyle, Petricone — now styled “Alex Rocco” — set up a meeting between Robert Mitchum and local Irish-American gangsters to help Mitchum research his part as Eddie Coyle, a low-level Irish-American criminal. Rocco introduced Mitchum to Howie Winter, leader of the Winter Hill Gang. Another Winter Hill Gang member who met with Mitchum was Johnny Martorano. Ironically, Martorano had murdered Billy O’Brien, a low-level gangster who may have been the prototype of the Eddie Coyle character.)

After his arrest, Petricone moved to California in 1962 and began using the name Alex Rocco. He first worked as a bartender in Santa Monica, California and took acting lessons from actor Leonard Nimoy, a fellow Boston native. Nimoy was not impressed with Rocco’s heavy Boston accent and told him to take speech lessons. Rocco followed through with Nimoy’s instructions and after ridding himself of the accent came back to study under Nimoy and character actor and teacher Jeff Corey.  Rocco played the part of Moe Greene, a Las Vegas casino owner, in the film The Godfather. Greene’s character represented the top Jewish mobster in Las Vegas; although he sought an Italian role, director Francis Ford Coppola remarked “I got my Jew!” on seeing Rocco. Other notable films in which Rocco appeared include The Wedding Planner, as Salvatore and appeared uncredited in Smokin’ Aces. In the film That Thing You Do!, Rocco played Sol Siler, the founder of Playtone Records.  In the fall of 1975, Rocco starred in the role of Pete Karras, a widowed father, writer, and photographer, in a 12-week CBS drama series Three for the Road, with Vincent Van Patten as his older son, John Karras, and Leif Garrett as his younger son, Endy Karras. After the death of their wife and mother, the Karrases sell their house, buy a recreational vehicle, and roam throughout the United States.

He played Charlie Polniaczek, Jo’s father on The Facts of Life. From 1989–90, Rocco was a regular on the television comedy series The Famous Teddy Z as “Al Floss”, a Hollywood talent agent. He received an Emmy Award as Best Supporting Actor in a Comedy Series for this role in 1990. In 1997, he appeared (along with Rodney Dangerfield) in the annual Thanksgiving episode of the ABC sitcom Home Improvement.  Rocco also had a recurring part in the long running animated series The Simpsons as the head of Itchy and Scratchy Studios, Roger Meyers, Jr. In DVD commentaries, Rocco expressed true gratitude to The Simpsons’ staff for allowing him his first voice-over role. He did further voice work on two early episodes of another Fox sitcom, Family Guy. Rocco did a voiceover on the 1998 Disney/Pixar film A Bug’s Life, deeming it his “greatest prize in life” as he was paid $1 million to record eight lines.  In 2008, he starred in Audi’s Super Bowl commercial for the Audi R8 supercar. The commercial was inspired by one of the films Rocco was in: The Godfather. He played a rich man who finds the front fascia of his luxury car in his bed, a nod to the scene from the original movie in which Jack Woltz, a rich movie producer, finds the head of his prized racehorse in his bed.  Rocco most recently was one of the stars of the Starz cable channel’s crime-drama series, Magic City. Rocco was scheduled to star as Mr. Marino in the Horror thriller film The Other.

After moving to Los Angeles, Rocco became a member of the Bahá’í Faith. He married Sandra Elaine Rocco (September 1, 1942 – June 12, 2002) on March 24, 1964. He adopted her son, director Marc Rocco (June 19, 1962 – May 1, 2009). They had a daughter Jennifer, lawyer, producer, writer, son Lucien, and a grandson Anthony Dominic Rocco, mother Jennifer. Sandra died of cancer, aged 59. Rocco later met and then married Shannon Wilcox on October 15, 2005.  Rocco died on July 18, 2015 of cancer in Studio City, Los Angeles.