Ralph Rexford Bellamy was born in Chicago, Illinois. He was the son of Lilla Louise (née Smith), a native of Canada, and Charles Rexford Bellamy. He ran away from home when he was 15 and managed to get into a road show. He toured with road shows before finally landing in New York. He began acting on stage there and by 1927 owned his own theater company. In 1931, he made his film debut and worked constantly throughout the decade both as a lead and as a capable supporting actor. He co-starred in five films with Fay Wray.  His film career began with The Secret Six (1931) starring Wallace Beery and featuring Jean Harlow and Clark Gable. By the end of 1933, he had already appeared in 22 movies, most notably Rebecca of Sunnybrook Farm (1932) and the second lead in the action epic Picture Snatcher with James Cagney (1933). He played in seven more films in 1934 alone, including Woman in the Dark, based on a Dashiell Hammett story, in which Bellamy played the lead, second-billed under Fay Wray. Bellamy kept up the pace through the decade, receiving a nomination for the Academy Award for Best Supporting Actor for his role in The Awful Truth (1937) with Irene Dunne and Cary Grant, and played a similar part, that of a naive boyfriend competing with the sophisticated Grant character, in His Girl Friday (1940). He portrayed detective Ellery Queen in a few films during the 1940s, but as his film career did not progress, he returned to the stage, where he continued to perform throughout the 1950s. Bellamy appeared in other movies during this time, including Dance, Girl, Dance (1940) with Maureen O’Hara and Lucille Ball, and the horror classic The Wolf Man (1941) with Lon Chaney, Jr. and Evelyn Ankers.

In 1949, Bellamy starred in the television noir private eye series Man Against Crime (also known as Follow That Man) on the DuMont Television Network; initially telecast live in its earliest seasons, the program lasted until 1956 and was simulcast for a season on Dumont and NBC, and ran on CBS during a different year. The lead role was taken by Frank Lovejoy in 1956, who subsequently starred in NBC’s Meet McGraw detective series.  Bellamy appeared on television in numerous roles over the following years. He was a regular panelist on the CBS television game show To Tell the Truth during its initial run. Bellamy starred as Willard Mitchell, along with Patricia Breslin and Paul Fix, in the 1961 episode “The Haven” of CBS’s anthology series The DuPont Show with June Allyson. About this same time, he also appeared on the NBC anthology series, The Barbara Stanwyck Show. In December 1961, he portrayed the part of Judge Quince in the episode “Judgement at Hondo Seco” on CBS’s Rawhide.  During the 1963–1964 television season, Bellamy co-starred with Jack Ging in the NBC medical drama The Eleventh Hour, in the role of a psychiatrist in private practice. Wendell Corey had appeared in the first season of the series.  Bellamy appeared on Broadway in one of his most famous roles, as Franklin Delano Roosevelt in Sunrise at Campobello. He later starred in the 1960 film version.

In the summer of 1961, Bellamy hosted nine original episodes of a CBS Western anthology series called Frontier Justice, a Dick Powell Four Star Television production. In 1950 Bellamy became a member of The Lambs, an actors club located in New York. Highly regarded within the industry, Bellamy served as a four-term President of Actors’ Equity from 1952–1964. On film, Bellamy also starred in the Western The Professionals (1966) as an oil tycoon married to Claudia Cardinale opposite adventurers Burt Lancaster and Lee Marvin, and Roman Polanski’s Rosemary’s Baby (1968) as an evil physician, before turning to television during the 1970s. Among many roles in numerous shows, sometimes as a series regular, Bellamy portrayed Adlai Stevenson in the 1974 TV-movie The Missiles of October, a treatment of the Cuban Missile Crisis. He was a member of the cast of the short-lived CBS espionage drama Hunter in 1977.  An Emmy Award nomination for the mini-series The Winds of War (1983) – in which Bellamy reprised his Sunrise at Campobello role of Franklin Roosevelt – brought him back into the spotlight. This was quickly followed by his role as Randolph Duke, a conniving billionaire commodities trader in Trading Places (1983) alongside Don Ameche. The 1988 Eddie Murphy film, Coming to America, included a brief cameo by Bellamy and Don Ameche, reprising their roles as the Duke brothers.  In 1984, Bellamy was presented with a Life Achievement Award from the Screen Actors Guild, and in 1987 he received an Honorary Academy Award “for his unique artistry and his distinguished service to the profession of acting”. In 1988, he again portrayed Franklin Roosevelt in the sequel to The Winds of War, War and Remembrance.  Among his later roles was a memorable appearance as a once-brilliant but increasingly senile lawyer sadly skewered by the Jimmy Smits character on an episode of L.A. Law. Bellamy continued working regularly and gave his final performance in Pretty Woman (1990).

Throughout the 1930s and ’40s, Bellamy was regularly seen socially with a select circle of friends known affectionately as the “Irish Mafia”, although they preferred the less sensational “Boy’s Club”. This group consisted of a group of Hollywood A-listers who were mainly of Irish descent (despite Bellamy having no Irish family connections himself). Others included James Cagney, Pat O’Brien, Spencer Tracy, Lynne Overman, Frank Morgan and Frank McHugh.  Bellamy was married four times: first to Alice Delbridge (1927–1930), then to Catherine Willard (1931–1945). On the occasion of his marriage to organist Ethel Smith (1945–1947), Time magazine reported, “”Ralph Bellamy, 41, veteran stage (Tomorrow the World) and screen (Guest in the House) actor; and Ethel Smith, 32, thin, Tico-Tico-famed cinema electric organist (Bathing Beauty); he for the third time, she for the second; in Harrison, N.Y.” Bellamy’s fourth wife was Alice Murphy (1949–1991; his death).  A Democrat, Bellamy was in attendance at the 1960 Democratic National Convention in Los Angeles.  Bellamy opened the popular Palm Springs Racquet Club in Palm Springs, California with fellow actor Charles Farrell in 1934.  On November 29, 1991, Bellamy died from a lung ailment, at Saint John’s Health Center in Santa Monica, California. He was 87 years old. Bellamy was buried in Forest Lawn – Hollywood Hills Cemetery in Los Angeles.