Borthwick had been skipper three times earlier in the year when tight-head prop Phil Vickery, who had led England to the 2007 World Cup final, was unavailable.
Vickery's starting spot was no longer secure in the face of competition from Matt Stevens and World Cup winner Johnson turned to a player who filled his second-row position.
Borthwick missed out on England's 30-man World Cup-winning squad five years earlier, but the 29-year-old had won 39 caps by the autumn of 2008.
"Steve is a good leader who always prepares thoroughly for matches at club and international level," Johnson said after promoting Borthwick to the captaincy.
"I will not be giving him a specific amount of time in the job, I just want to support him as much as possible."
Borthwick had a baptism of fire in the role with Twickenham Tests against South Africa, Australia and New Zealand after an opening 39-13 victory over the Pacific Islanders.
All three games against the southern hemisphere super-powers were lost in one-sided fashion, and Borthwick faced fierce criticism from fans and the media.
But Johnson kept faith with him and Borthwick guided England to second place in the 2009 Six Nations Championship.
Borthwick was confirmed as captain for the 2010 Six Nations, in which England finished third, but he sat out the final game against France after aggravating an ongoing knee injury.
He missed the summer tour to Australia and never played for England again, finishing with 57 caps and having captained the side 21 times.
England won the 2011 Six Nations title, but Johnson resigned the following November after a poor performance on and off the field at the 2011 World Cup in New Zealand.