At a private ceremony in London, Welsh told those in attendance of his friendship and bond with the Edinburgh-born popstar, reports the Daily Record.
McKeown’s wife Peko and son Jubei, who also delivered a tribute, celebrated his life with close friends and family.
During the order of service they listened to a version of the classic Danny Boy, recorded by McKeown with Vanessa Ann Redd, and one of his most recent songs called Goodbye.
A close friend of the family told the Record: “Those two songs did the trick and set everybody off, but it was a celebration of Les’s life and Irvine was brilliant. Irvine told how he had become friends with Les over the years. There was a lot of laughter.”
McKeown, who was the frontman of the Bay City Rollers during their heyday in the 1970s, died last month at the age of 65.
Formed at the end of the 1960s, the Bay City Rollers enjoyed huge success at home and abroad with their distinctive tartan outfits and upbeat pop tunes like Bye Bye Baby and Shang-a-Lang.
They had a massive teen following and sold more than 100 million records.
They broke through into the mainstream in 1974 after a series of singles which failed to dent the charts.
Alongside McKeown and Alan Longmuir, who died aged 70 in 2018, the classic line-up also included guitarists Eric Faulkner and Stuart Wood, with Longmuir’s younger brother Derek on drums.
McKeown was born in Edinburgh to Irish parents and joined the Bay City Rollers in late 1973, replacing founding lead singer Gordon “Nobby” Clark, who had become disillusioned with the band’s musical direction.
His arrival coincided with the Bay City Rollers’ ascent to fame and McKeown remained lead vocalist until 1978, appearing on Top Of The Pops on a number of occasions.
After the funeral on Sunday, Irvine Welsh wrote on Twitter: “Honoured to be asked by the family to give a tribute to an old friend. Goodbye bud, you spread a lot of joy.”