Johnson, 28, only arrived at Molineux last month in a £4.5 million deal from Birmingham, while Henry has been at the club for three years, but McCarthy believes his new centre-back's leadership qualities make him an oustanding candidate.
"I've decided to make the change and pass the armband on to Roger," McCarthy said. "I've been looking to bring in a commanding defender who is vocal and a leader and, having done that with Roger, I've decided to make him captain.
"I think it can be easier to captain the side from that position in the centre of defence, where you can see everything in front of you and are perfectly placed to organise the team. It's a job Roger knows well and has carried out successfully in the past, and I think his leadership qualities will be a benefit to everyone."
Johnson captained fomer clubs Cardiff and Wycombe and will skipper Wolves for the first time in this Saturday's friendly with Real Zaragoza.
And McCarthy does not anticipate any fall-out from taking the armband off Henry, who the Wolves boss insists will continue to play a "key" role in the first team.
"I would like to thank Karl who has been our captain since taking over during the promotion season." McCarthy added.
"He's carried out the job diligently and professionally and will continue to be a key member of my team as we head into our third season in the Premier League."