Johnson, who turns 31 this week, did not play a match for the Scorchers last season due to injury and while he remains committed to playing for Western Australia in the longer form of the game, joining the Heat for the BBL will allow him to spend some time in his former home state of Queensland.
"I'm enjoying my cricket with the Warriors and signing with the Heat means I can have a chance to keep playing through December and January, which is the time of year you want to be in action and performing," Johnson said. "I enjoyed the challenge with the Mumbai Indians in the IPL and at the Champions League and I was happy with how I went for Australia in the ODI series in Dubai during the winter.
"I'm really looking forward to playing at the Gabba once more and catching up with the boys again. There was a lot of good cricket played last season in the BBL and I think everyone who saw the Sixers win the Champions League this week would agree that that standard of the competition is excellent."
Johnson has slipped down in Australia's Test fast-bowling queue since he last played in the baggy green in November last year, but the national selector John Inverarity indicated on Monday he would remain in the selectors' thoughts this summer. Should Johnson pile up the wickets in the Sheffield Shield over the next few weeks he will provide the selectors with another option.
"Mitchell Johnson, in the first two Shield games in Perth, his action was good and he bowled very well," Inverarity said. "Michael [Clarke] made 60-odd against him and thought he bowled very well."
Johnson moved from Queensland to Western Australia in 2008 to be with his then-girlfriend Jessica Bratich, who was based in Perth. The couple are expecting their first baby, due in early December.