He is playing his first tournament since suffering serious injuries in a car accident in December 2022 that kept him out of last year's IPL as well as the 50-overs World Cup in India
The 34-year-old replaces David Wiese who will be out for six weeks with a fractured finger, the selectors announced on Saturday.
It raises the possibility of a first international appearance in 18 months for powerful hitter Morkel who will also reach 50 caps in the 20-over format if he plays.
Batsman Rilee Rossouw will miss the five-match one-day series that follows and has been replaced by uncapped Khaya Zondo who is also in the T20 squad.
South Africa will also play four Tests on what is their longest ever tour to the sub-continent.