Scotland International Stewart featured in last year's sprint series for the Bulls through the Glasgow Warriors pro draft and joins permanently following a stint with Connacht.
Stewart could line up against some familiar faces when the competition kicks-off next Friday with the Bulls hosting a Glasgow Warriors A team at Millbrae.
Ayrshire Bulls Squad:
Alex McGuire
Amena Caqusau
Andrew Nimmo
Andy Stirrat *
Antony Fitch
Archie Smeaton *
Ben Afshar *
Blair Jardine
Blair Macpherson
Bobby Beattie
Calvin Henderson
Chris Elliot
Christian Townsend *
Craig Miller
Edward Bloodworth
Eli Caven
Ewan Bulger
Frazier Climo
Grant Baird
Grant Stewart
Jamie Drummond *
Jamie Shedden
Kerr Yule
Lewis McNamara
Luca Bardelli
Reiss Cullen
Richie Simpson
Rory Jackson
Ryan Sweeney
Scott Clelland
Scott Watson
Thomas Glendinning
Tim Brown
William Farquhar
*FOSROC Scottish Rugby Contracted Academy Players. These players will also be available for selection to Glasgow Warriors A in the first three rounds of competition.
Among the players from last season's squad to have moved on are James Malcolm, who has returned to the states to resume his MLS career. Jordan Lenac is currently playing in Portugal. Cameron Jones has joined the Heriot's squad and Will Hunt has returned home and is currently playing in England.