He grew up in the East Tremont section of The Bronx, the son of Russian Jewish immigrants; his father, Max, was a doctor, and his mother, Jessie, was a nurse. A graduate of Columbia University and Harvard Law School, he received a master's degree in aviation law from Northwestern University in 1949.

Wager was best known as an author of mystery and spy fiction; his works included 58 Minutes (1987), whose story was used as the basis of the action film Die Hard 2 in 1990. Two of his other novels became major motion pictures in 1977: Viper Three (1972), which was released as Twilight's Last Gleaming, and Telefon (1975). Wager wrote a number of original novels in the 1960s under the pseudonym "John Tiger" that were based on the TV series I Spy and Impossible.

Prior to making his reputation as a novelist, Wager was a Fulbright Fellow at the Sorbonne in Paris and diplomatic adviser to Israel's Director of Civil Aviation. He was also a writer and producer for CBS Radio, CBS television, and NBC television and was editor-in-chief at Playbill from 1963 to 1966. In addition, Wager worked in public relations for ASCAP and the University of Bridgeport.

He died in 2004 at Amsterdam House, a home for the elderly in Manhattan.

Winifred McIvor Wager: married June 4, 1975 - July 11, 2004 (his death)Sylvia Leonard Wager: married May 6, 1952 - May __, 1975 (divorced; one child)

• Death Hits the Jackpot (1954)
• Operation Intrigue (1956)
• I Spy (1965)
• I Spy #2: Masterstroke (1966)
• I Spy #3: Superkill (1967)
• I Spy #4: Wipeout (1967)
• I Spy #5: Countertrap (1967)
• I Spy #6: Doomdate (1967)
• Mission: Impossible (1967)
• I Spy #7: Death-Twist (1968)
• Mission: Impossible #4: Code Name Little Ivan (1969)
• Sledgehammer (1970)
• Warhead (1971)
• Viper Three (1972), adapted for film as Twilight's Last Gleaming (1977)
• Swap (1973)
• Telefon (1975), adapted for film as Telefon (1977)
• Time of Reckoning (1977)
• Blue Leader (1979)
• Blue Moon (1981)
• Blue Murder (1982)
• Designated Hitter (1982)
• Otto's Boy (1985)
• Raw Deal, novelization of the Arnold Schwarzenegger film (1986)
• 58 Minutes (1987), adapted for film as Die Hard 2 (1990)
• The Spirit Team (1996)
• Tunnel (2001)
• Kelly's People (2002)

The I Spy and Mission: Impossible books were published under the name "John Tiger." Operation Intrigue (1956) was published under "Walter Hermann."