Waller died Friday at The William W. Backus Hospital in Norwich, Conn., nursing supervisor Nity Oris confirmed Monday. The duo's Web site says Waller, who lived in Ledyard, Conn., went into cardiac arrest Thursday night, and the state medical examiner's office lists his cause of death as cardiovascular disease.
Waller and Peter Asher hit No. 1 on music charts around the world in 1964 with their debut single A World Without Love. McCartney, who at the time was dating Asher's sister, actress Jane Asher, wrote the song.
The duo also hit the charts with other songs written by McCartney, including Nobody I Know and I Don't Want To See You Again. Although McCartney wrote the songs, they were jointly credited to him and John Lennon, as was all their work at the time.
Peter and Gordon's other hits included their versions of Del Shannon's I Go to Pieces and the Buddy Holly song True Love Ways, both in 1965; Lady Godiva, 1966; and Knight in Rusty Armour reached the top 20 in 1967.
Woman, another McCartney song not to be confused with Lennon's later song of the same name -- also reached the top 20 in 1966.
According to the book The Beatles: The Biography by Bob Spitz, McCartney had started writing A World Without Love as a teenager. By the time the Beatles reached the top in 1963-64, it wasn't up to their current standard, and it had also been rejected by another singer as too soft.
McCartney then rewrote it a bit and gave it to Asher. He and Waller sang it with a pleasant laid-back yearning that transformed the song into a perfectly acceptable pop hit, Spitz wrote.
Peter Asher's Web site says Peter and Gordon had nine Top 20 records from 1964 until they split in 1968.