After graduating from Boston College, he won election to the Massachusetts House of Representatives, where he became a strong advocate of Franklin D. Roosevelt's New Deal policies.

O'Neill broke with President Lyndon B. Johnson on the Vietnam War in 1967 and called for Richard Nixon's resignation in light of the Watergate scandal.

With the election of President Jimmy Carter, O'Neill hoped to establish a universal health care system and a guaranteed jobs program.

As a senior at Boston College, O'Neill ran for a seat on the Cambridge City Council, but lost; his first race and only electoral defeat.

"[2] After graduating in 1936, O'Neill was elected at the age of 24 to the Massachusetts House of Representatives, aided by tough economic times among his constituents; the experience made him a strong advocate of the New Deal policies of Roosevelt, which were just then coming to an end.

His biographer John Aloysius Farrell said his background in Depression-era working-class Boston, and his interpretation of his Catholic faith, led O'Neill to view the role of government as intervening to cure social ailments.

[17] After wrestling with the issues surrounding the Vietnam War, in 1967 O'Neill broke with President Lyndon B. Johnson and came out in opposition to America's involvement.

As Majority Leader, O'Neill was the most prominent Democrat in the House to call for the impeachment of President Richard M. Nixon in light of the Watergate scandal.

However, the Democrats lacked party discipline, and while the Carter administration and O'Neill started out strong with the passage of ethics and energy packages in 1977, there were major stumbles.

O'Neill was also dismayed by Carter's frugal behavior in cutting executive staff and reducing the scale of White House entertainment.

A continually weakening economy and the Iran hostage crisis made prospects bleak for Carter and the Democrats in the 1980 congressional and presidential elections.

O'Neill even went as far as calling Ronald Reagan "the most ignorant man who had ever occupied the White House,"[4] "Herbert Hoover with a smile", and "a cheerleader for selfishness."

However, O'Neill gave tacit approval to Democratic congressman Charlie Wilson to implement the Reagan Doctrine in the Soviet-Afghan war.

On October 21, 1986, O'Neill, representing President Reagan, threw out the ceremonial first pitch at Game 3 of the 1986 World Series, played at Fenway Park.

Beginning with the "Saint Patrick's Day declaration" in 1977, denouncing violence in Northern Ireland and culminating with the Irish aid package upon the signing of the Anglo-Irish Agreement in 1985, the "Four Horsemen", as they were called, convinced both Carter and Reagan to press the British government on the subject.

The book also helped turn him into a national icon, and O'Neill starred in a number of commercials, including those for Trump Shuttle, Commodore Computers, Quality International Budget Hotels and for Miller Lite, in which he appeared with Bob Uecker.

Critics, however, noted some inaccuracies with his book such as his views of the Grenada invasion conflicting with his public opinions of the time, David Powers questioning that John F. Kennedy's aide Kenneth O'Donnell allegedly heard more shots during his assassination in a conversation with O'Neill, and Senator Barbara Mikulski saying that "Tip has his memoirs mixed up," regarding opposition towards O'Neill endorsing Geraldine Ferraro in the 1984 vice presidential election.

Four years before his retirement, he had a cameo role in the February 17, 1983, episode of Cheers entitled "No Contest," which featured him ducking into the bar to escape Diane Chambers, who had pestered him on the street about his political ideals.

He appeared in an episode of the NBC sitcom Silver Spoons, which featured him delivering a mock press conference praising recurring character Freddy Lippincottleman's efforts on behalf of the homeless.

His oldest son and namesake, Thomas P. O'Neill III, a former lieutenant governor of Massachusetts, works in public relations in Boston.

[4] President Bill Clinton paid tribute to him, saying, "Tip O'Neill was the nation's most prominent, powerful and loyal champion of working people...

The one-man biographical play, written by longtime Boston sportswriter Dick Flavin, features O'Neill telling stories of his life, from his childhood to after his retirement in politics.

[38] O'Neill himself contributed several oral history interviews to its archives chronicling his work for the Democratic party and friendship with President Kennedy.