While studying at Guildhall, he was asked by Laurie Holloway to play piano on an international tour with his wife Marion Montgomery.
Edmonstone worked with Holloway on the first three series of the BBC1 television show Strictly Come Dancing, where he played piano and arranged a portion of the music.
He has been a member of Mike Walker's Madhouse band and has played with Mark Lockheart, Stan Sulzmann, and Iain Dixon.
At the 19th meeting of the International Association of Schools of Jazz, Dave Liebman invited him to play in his only appearance during that conference.
As a session musician he has performed with Rick Astley, Gary Barlow, Michael Ball, Dame Shirley Bassey, Tony Bennett, Alfie Boe, Madeline Bell, Tommy Blaize, Michael Bolton, Tony Christie, Sir John Dankworth, Bruce Forsyth, Robin Gibb, Mark King, Dame Cleo Laine, Kenny Lynch, David McAlmont, Katie Melua, Liza Minnelli, Tony Momrelle, Donny Osmond, Cliff Richard, Heather Small and Ruby Turner.