Schwartz was born in New York City, the son of composer Arthur Schwartz (1900–1984) and 1930's Broadway ingénue Kay Carrington. Though his memoirs describe an unhappy childhood, Schwartz grew up animated by a passionate interest in musical arts. His father was a composer of Broadway and film scores ("Dancing in the Dark" and "That's Entertainment!" are among his works), and from an early age Schwartz developed his interest through this family perspective. Jonathan's half-brother Paul Schwartz (born 1956) is a composer, conductor, pianist, and producer.
Schwartz worked at New York's WNEW-FM from 1967 to 1976, followed by stints at WNEW, WQEW, and since 1999 WNYC-FM. Schwartz also served as programming director for XM Satellite Radio's now-defunct High Standards channel from 2001 to 2008, and appeared on Sirius XM's Siriusly Sinatra and '40s on 4 channels from 2008 to 2013.
Schwartz is best known for The Jonathan Schwartz Show, which airs Saturday evenings and Sunday afternoons on WNYC-FM, and comprises about half talk and half an eclectic mix of music.
In his talk during the shows, Schwartz will discuss famous pop songwriters and singers, and jazz artists. His music selections incorporate pop jazz, pop standards, big band and Broadway show tunes, augmented by music of nearly any popular style that has influenced twentieth century American tastes. His playlists reflect the "Great American Songbook" or, as Schwartz describes it, "America's classical music". Traditionally, Schwartz opens each broadcast with the same secret snippet of music which he had always refused to identify until 2014, at a show at the Brooklyn Academy of Music: slightly more than a minute of "a lilting woman's voice, wordless and yet evocative, over an acoustic guitar." The voice is that of Schwartz's friend since childhood, Carly Simon; listeners had speculated that the music may have been composed by his father, but it was a joint work of his and Carly Simon's. Similarly, he closes most shows with a song from the late cabaret singer Nancy LaMott, followed by a segment from another instrumental recording by Schwartz's idol, the late Nelson Riddle, and his orchestra.
Schwartz is known for his on-air stories about his interactions with famous people, most often Frank Sinatra. He is also known for his encyclopedic knowledge of Sinatra, who was reportedly amazed by Schwartz's knowledge of every song he had ever recorded. He champions young artists who carry on the traditions of the American Songbook, as well as reveling rapturously in the songwriters and performers of the Sinatra era. In 1986 Schwartz won a Grammy Award for Best Album Notes for The Voice - The Columbia Years 1943-1952.
In 2013 WNYC launched The Jonathan Channel, a 24/7 streaming Internet radio station programmed by Schwartz and dedicated to American songs selected by him. The channel also features live programming hosted by Schwartz, along with simulcasts and replays of his Saturday and Sunday WNYC shows.
In addition to his radio work, Schwartz has performed in New York City cabaret, recorded three albums as a singer, and authored five books:Almost Home (13 short stories), 1970 Doubleday
Distant Stations (a novel), 1979 Doubleday
The Man Who Knew Cary Grant (a novel), 1988 Random House;
A Day of Light and Shadows (about one baseball game), 2000 Akadine Press
All in Good Time (a memoir), 2004 Random House
He does most of his writing in Palm Springs, California.
Schwartz was briefly married to the author Sara Davidson in the late 1960s. He married the journalist and Vanity Fair correspondent Marie Brenner in 1979, with whom he has one daughter. Schwartz later married Elinor Renfield, with whom he has a son.
In March 2010, Schwartz married actress Zohra Lampert in New York City. At the wedding, his long-time friend Tony Bennett sang "I See Your Face Before Me", a 1937 composition by Schwartz's father and Howard Dietz.