Johnston has stated that, for him, the "I" in the song is God, and that songs come from the spirit of creativity in all of us. He has said that the song is not about his Beach Boys bandmate Brian Wilson.
Manilow was initially reluctant to record the song, stating in his autobiography Sweet Life: "The problem with the song was that if you didn't listen carefully to the lyric, you would think that the singer was singing about himself. It could be misinterpreted as a monumental ego trip." After persuasion by Clive Davis, then president of Arista Records, Manilow recorded the song, and his version of "I Write the Songs" was the first single taken from the album Tryin' to Get the Feeling. It first charted on the Billboard Hot 100 on November 15, 1975, reaching the top of the chart nine weeks later, on January 17, 1976.
Manilow performed another shortened version of this song with Stephen Colbert when he was a guest on The Colbert Report on October 30, 2006.
After his version reached number one, Manilow himself composed a novelty song based on this song which he recorded under the title "I really do write the songs" in which he sings about how he composes each part of a song and the line "sometimes I really do write the songs" at the end of each verse. In the finale he sings, "sometimes...ah, what the hell...I write the songs." Unreleased at the time, it was included as a bonus track on the reissue of his album This One's for You in 2006.