His father, Abram, was a grocery store owner from Kyiv[5][6] and his mother, Feiga "Fanny" Grundman, from a shtetl called Lashanovka in Volhynia (now Ukraine).

[7] He was an all-state football end and member of the Ames High School state championship basketball and track teams of 1955.

He lost a 1970 campaign to unseat Republican Congressman Fred Schwengel in Iowa's 1st congressional district by only 765 votes (out of over 120,000 cast).

[8] During his first term in Congress, he sat on the House Judiciary Committee and voted for the impeachment of President Richard Nixon for his activities in the Watergate scandal.

He was one of eight Democratic members of the committee who voted for all five articles of impeachment drafted against Nixon; three were reported to the House, while two failed.

Six months into his first term in Congress, Mezvinsky separated from his wife of ten years Myra Shulman; they were divorced two weeks after his 1974 re-election.

[12] Mezvinsky unsuccessfully sought the Democratic nomination for the United States Senate seat held by retiring incumbent Republican Richard Schweiker in 1980, but lost to former Pittsburgh Mayor Pete Flaherty.

[13] Mezvinsky became chairman of the Pennsylvania Democratic Party, and made a run for state attorney general in 1988.

Mezvinsky, who had been working as an attorney at the time, was funneling embezzled and fraudulently obtained money to West African con men after falling victim to an online advance-fee scam.

Shortly after Mezvinsky's indictment, he was diagnosed with bipolar disorder, but the judge at his trial disallowed a mental illness defense.