John Denver wrote and recorded "Leaving on a Jet Plane" in 1966 when he was just 23 years old. It was included on his debut demo recording as "Babe, I Hate to Go". He made copies and gave them to friends as Christmas presents that year. John's producer Mel Okun convinced him to change the title to "Leaving on a Jet Plane" in 1967. Peter, Paul, and Mary had a hit with the song in 1969, and Denver recorded the song again for his debut studio album "Rhymes and Reasons", released as a single in October 1969. Though it is still one of Denver's best-known songs, the single failed to appear on the charts for him. The Peter, Paul, and Mary version was released as a single in 1969 and became their only No. 1 on the Billboard Top 100. It was also their last hit record and the only version of "Leaving on a Jet Plane" that ever charted.

Source: The Great American Songbook Foundation