Finney was born in Milwaukee, Wisconsin and given the name John Finney. After his father died when he was three years old, he was renamed Walter Braden Finney in honor of his father, but continued to be known as "Jack" throughout his life. He attended Knox College in Galesburg, Illinois, graduating in 1934. He married Marguerite Guest and they had two children, Kenneth and Marguerite. After living in New York City and working for an advertising agency there, he moved with his family to California in the early 1950s. He lived in Mill Valley, California, and died of pneumonia and emphysema in Greenbrae, California.

Finney's first short story, "The Widow's Walk", won a contest sponsored by Ellery Queen's Mystery Magazine in 1946. His first novel, 5 Against the House, was published in 1954. It was made into a movie the following year.

Finney's novel The Body Snatchers (1955) was the basis for the 1956 movie Invasion of the Body Snatchers (and its remakes). It tells the story of aliens who invade Earth by emerging from pods and taking over the bodies of humans.

Another novel, Assault on a Queen (1959), became a film with Frank Sinatra as the leader of a gang that pulls a daring robbery of the RMS Queen Mary.

Finney's greatest success came with his science fiction novel Time and Again (1970). Its protagonist, Simon Morley, is working in advertising in New York City when he is recruited for a secret government project trying to achieve time travel. Instead of using a physical machine, the participants steep themselves in the history and culture of a particular time and place, then travel there through hypnosis or self-hypnosis. Morley travels to the New York City of 1882. The novel is notable for Finney's vivid and detailed picture of life in the city at that time. Morley sees many actual historical sites, some now gone (e.g., the post office that, until 1939, stood in what is now the southern tip of City Hall Park) and some still existing (e.g., St. Patrick's Cathedral, then the tallest building in its Fifth Avenue neighborhood).

In 1987, Finney was given the World Fantasy Award for Life Achievement at the World Fantasy Convention, held in Nashville, Tennessee.

Finney's story "Such Interesting Neighbors" was made into an episode of the Spielberg-created anthology series Amazing Stories and starred Adam Ant and Marcia Strassman.

In 1995, twenty-five years after Time and Again, Finney published a well-received sequel called From Time to Time featuring the further adventures of Morley, this time centering on Manhattan in 1912. Finney died at the age of 84 not long after finishing the book.

The 1998 television movie The Love Letter, starring Campbell Scott and Jennifer Jason Leigh, is based on Finney's short story of the same name, which appeared in The Saturday Evening Post (1959).

The Third Level, Knox College's science fiction and fantasy publication, is named for Finney's short story and collection.

• "Someone Who Knows Told Me ", Cosmopolitan (Non-Fiction) (December, 1943)
• "The Widow's Walk", Ellery Queen's Mystery Magazine (July, 1947)
• "Breakfast in Bed", Collier's (May, 1948)
• "The Little Courtesies", Collier's (June, 1949)
• "A Dash of Spring", Cosmopolitan (June, 1949)
• "I Like It This Way", Collier's (June, 1950)
• "My Cigarette Loves Your Cigarette", Collier's (September, 1950)
• "Such Interesting Neighbors", Collier's (January, 1951)
• "One Man Show", Collier's (June, 1951)
• "I'm Scared", Collier's (September, 1951)
• "It Wouldn't be Fair", Ellery Queen's Mystery Magazine (November, 1951)
• "Obituary" (co-written with C.J. Durban), Collier's (February, 1952)
• "Quit Zoomin' Those Hands Through the Air", The Magazine of Fantasy and Science Fiction (December, 1952)
• 5 Against the House (Novel) (1954)
• Of Missing Persons (1955)
• The Body Snatchers (Novel) (1955)
• "Man of Confidence", Good Housekeeping (September, 1955)
• "Second Chance", Good Housekeeping (April, 1956)
• Telephone Roulette: A Comedy in One Act (1956)
• "Contents of the Dead Man's Pocket", Good Housekeeping (June, 1956)
• The House of Numbers (1957)
• The Third Level (1957) (short story collection), in England as The Clock of Time (1958)
• Assault on a Queen (Novel) (1959)
• "The Love Letter", Saturday Evening Post (August 1, 1959) [Also re-published in January/February 1988 issue of Saturday Evening Post]
• "The U-19’s Last Kill", Saturday Evening Post (six-part series, beginning August 22, 1959 and ending September 26, 1959)
• "The Other Wife" (aka The Coin Collector), Saturday Evening Post (January 30, 1960)
• "An Old Tune" (aka Home Alone), McCall's (October, 1961)
• "Old Enough for Love", McCall's (May, 1962)
• "The Sunny Side of the Street", McCall's (October, 1962)
• Hey, Look at Me! (1962)
• Lunch Hour Magic (1962)
• "Time Has No Boundaries" (aka The Face in the Photo), Saturday Evening Post (October 13, 1962)
• Where the Cluetts Are (1962)
• Good Neighbor Sam (1963)
• I Love Galesburg in the Springtime (1963) (short story collection)
• This Winter's Hobby: A Play (1966)
• The Woodrow Wilson Dime (1968)
• Time and Again (Novel) (1970)
• Marion's Wall (1973)
• The Night People (1977)
• Forgotten News: The Crime of the Century and Other Lost Stories (1983) (Nonfiction)
• About Time (1986) (short story collection)
• Three by Finney (1987) (an omnibus edition of The Woodrow Wilson Dime, Marion's Wall, and The Night People)
• From Time to Time (Novel) (1995)

Films based on Finney's novels and stories

• 5 Against the House (1955 Phil Karlson film starring Guy Madison, Kim Novak, and Brian Keith)
• Assault on a Queen (1966 Jack Donohue film based on The U-19's Last Kill starring Frank Sinatra, Virna Lisi, and Anthony Franciosa)
• Invasion of the Body Snatchers (1956)
• The House of Numbers (1957 Russell Rouse film noir starring Jack Palance)
• Good Neighbor Sam (1964 David Swift film starring Jack Lemmon, Romy Schneider, and Dorothy Provine)
• Invasion of the Body Snatchers (1978 remake)
• Maxie (1985 Paul Aaron film starring Glenn Close, Mandy Patinkin, and Ruth Gordon; based on Marion's Wall)
• Body Snatchers (1993 remake of Invasion of the Body Snatchers)
• The Love Letter (1998 Dan Curtis TV movie starring Campbell Scott, Jennifer Jason Leigh, David Dukes, and Estelle Parsons; based on the story of the same name)
• The Invasion (2007 remake of Invasion of the Body Snatchers)

The 1980 film, Somewhere in Time, was based on a novel by another author, but used the same time travel technique described by Finney in Time and Again and About Time.