Borthwick will be Durham's third captain in as many seasons. Cameron Bancroft led the side in the first half of 2019 before he was included in Australia's Ashes squad. Ned Eckersley then took over the role, and continued through the Bob Willis Trophy campaign in 2020.
While his captaincy experience is limited to a couple of games for Surrey's second XI, Borthwick will be a senior player in Durham's squad, and Marcus North, the club's director of cricket, said that he hoped he could demonstrate that within the role.
"There is no doubt Scott brings a huge amount of playing experience to the table," North said. "This is a great opportunity for Scott to draw upon these and transfer those experiences into a formal leadership role."
Borthwick said that captaining his boyhood club had been a long-term ambition of his.
"Just coming back to play for Durham again has been an amazing experience for me, so to be asked to captain the team is a huge honour," he said. "Leading out the Durham team has been something I've dreamt about since I was a kid in the academy so it's a really special thing for me.
"The coaches and management team have been really welcoming since I re-joined the club and I'm looking forward to working closely with them. We've got an exciting group of players with lots experience and I look forward to leading the team to success."
The club are yet to name a captain for either white-ball format. Nathan Rimmington led the T20 Blast side in 2020 but has since left the club, while Stuart Poynter and Paul Coughlin have both captained in recent T20 seasons.