The classic gameshow, which was most famously presented by Roy Walker in the '80s and '90s, has been the subject of reboot rumours for some time, with the broadcaster's interest in the iconic format first reported in May.
STV Productions is now advertising for audience members for a pilot recording, which will feature Britain's Got More Talent presenter Mulhern as the host.
The original format will remain, although the show will be updated with new 3D graphics and a new concluding game, reports Broadcast.
Mulhern's pilot will be filmed in London on August 27.
Catchphrase originally ran for more than 300 episodes on ITV from 1986 to 2002.
