His deal is believed to be below maximum contract earnings in Perth's 18-man squad, with Johnson potentially used by Cricket Australia through additional services for extra earnings with promotional and marketing advantages for the entire T20 competition.

Any longer-term commitment to the annual limited-overs tournament played through December and January will be considered after Johnson gets through his initial season as a Scorcher.

He has played with WA at Sheffield Shield level since moving to Perth from Queensland in 2008.

Johnson's decision to join the successful Perth outfit offsets a controversial decision early this month from popular Scorchers cult hero Brad Hogg.

The 45-year-old left-arm wrist spinner has been the Scorchers' biggest drawcard and such an astonishing bowling performer that he was recalled to Australia's T20 team.