Morkel will join the Scorchers squad from next week and will be available for selection for the last home-and-away fixture on Sunday 26 January in Sydney.
The towering quick has played in 86 Tests, 117 ODIs and 44 T20 Internationals for the Proteas, with 544 international wickets to his name.
In a successful international career spanning 12 years he became the fifth bowler for South Africa to take 300 Test wickets.
Head Coach Adam Voges said;
“Once we knew CJ (Chris Jordan) had been picked in the England side we knew that we would need a replacement for the back end of the tournament and Morne was always at the top of the list.
“He brings a wealth of experience and has performed really well particularly in the Mzansi Super League in South Africa where he was one of the leading wicket takers.
“He was really keen to come on board. Luckily I’ve played a bit with Morne over the years so we’ve got a good relationship and he was super excited to get involved in the Big Bash.
“I think CJ has been fantastic for us, not only what he’s brought with the ball but just the way that he’s been around the group. His experience has helped the guys out on the field and he’s helping Mitch with his leadership as well. We wanted someone of a similar calibre to come in and I think Morne will do a great job with that and continue the good work that CJ has done.
“We’re going to get Morne to Perth next week and he’ll be around the group for a week or so before he plays so that will be great for him to get to know everyone and hopefully make that transition a bit smoother.”