The 30-year-old defender, who joined Saints in 2004, takes over from Dave Mackay who retired last week due to an on-going hip issue.
Manager Tommy Wright told the club’s official website: “It was an easy decision for me. Steven is the longest-serving player at the club, a leader on the pitch and is perfect to follow in Dave’s footsteps.”
Chris Millar and Brian Easton will remain as joint vice captains.
Wright could be tempted to hand teenager defender Aaron Comrie a start at Pittodrie tonight. With former Aberdeen skipper Richard Foster cup tied, Mackay hanging up his boots and Keith Watson and Tam Scobbie still sidelined by injury, the St Johnstone boss faces a selection headache for tonight’s Betfred Cup clash.
One-time Celtic youngster and Montrose loan star Comrie, 19, was on the bench in the 1-0 win over Hearts.
Wright said: “With Richard out of the reckoning we are a bit light defensively but we have one or two options.
“Aaron is a possibility as a natural right-back. But David Wotherspoon has played right back at Aberdeen before and Blair Alston is another option.”
Midfielder Chris Millar comes back into the reckoning after missing the Hearts game after a training ground knock. Winger Danny Swanson is also available after shaking off a thigh strain.
Wright said: “This is the tie of the round with all the potential to be a cracking cup tie. These are two teams who know each other quite well. It will be a difficult game for both sides.
“It is as tough a tie as we could get, particularly being away. But our away form has been good and Aberdeen seem to bring the best out in us.”