Maharaj represented Durban's Super Giants in the previous three seasons of the tournament but was bought by the Capitals at the player auction in September.
The Pretoria franchise said in a statement: "Maharaj brings a wealth of international pedigree across formats, along with a proven track record of guiding teams with composure, clarity and intent.
"Having captained South Africa in white-ball cricket and served as a senior figure within the national setup for several years, Maharaj's leadership experience, tactical understanding and consistency make him an invaluable addition in this role.
"His presence strengthens the balance and direction of the Pretoria Capitals squad as the team heads into the new season."
The latest appointment continues the Capitals' revamp of the squad and the coaching staff ahead of the new campaign.
India legend Sourav Ganguly has been installed as the franchise's new head coach and will be assisted by former Proteas skipper Shaun Pollock.
The Capitals then splashed the cash in the player action, acquiring Dewald Brevis for a record amount of R16.5 million while adding Lungi Ngidi, Lizaad Williams, Craig Overton, Saqib Mahmood and Codi Yusuf, among others, while Andre Russell was a wild card signing.
The fourth season of SA20 kicks off on Boxing Day when defending champions MI Cape Town take on Durban's Super Giants at Newlands.
The Capitals kick off their new campaign on 27 December when they host Joburg Super Kings in Centurion.
South Africa needed a second Super Over against Afghanistan to emerge victorious in one of the most drama-filled T20 World Cup matches ever played in Ahmedabad on Wednesday.
Sunrisers Eastern Cape underlined their status as SA20's dominant force with a nerve-shredding six-wicket victory over Pretoria Capitals at Newlands, clinching a third title in four seasons.
Sunrisers Eastern Cape sailed into yet another SA20 final after beating the Paarl Royals by seven wickets in a low-scoring encounter at the Wanderers on Friday.
Lhuan-dre Pretorius found his form at the perfect moment as Paarl Royals ended Joburg Super Kings' SA20 campaign with a commanding 36-run win at Centurion on Thursday night.
