Fundraiser Antonio Cortes, 32, donned the DC Comics superhero outfit as part of a charity collection.
While taking a break in a pub in Gloucester city centre, Mr Cortes said he heard screams and ran outside to see a man trying to mug a woman.
He told the BBC he chased the attacker and wrestled him to the ground until police arrived.
"I could see the woman was distressed and thought 'something has to be done' so I just went with it," said Mr Cortes, a trained Thai boxer.
Police officers attended minutes later and took the man away.
Mr Cortes said when they saw how he was dressed there "were a few laughs and giggles".
It was a scene reminiscent of BBC sitcom Only Fools and Horses, when Del Boy and Rodney unwittingly foiled a robbery.
In the 1996 Christmas special, the pair were heading to a party dressed as Batman and sidekick Robin when their Reliant Regal van broke down on the way.
They walked the rest of the way and, as they emerged from fog in costume, they scared away thieves attempting to mug a councillor.
Mr Cortes was in the city as part of his job working for social enterprise Give A Smile UK, which raises awareness of disabled children and sends them and their families on respite holidays all year round.
Immediately after the incident the lady, who he thought appeared to be about 60, was taken into the Co-Operative bank by staff to be looked after.
Later he saw her with her husband, who came over, shook his hand and said thank you.
"It's very rewarding - a good thing and I feel good for it definitely," he said.
Gloucestershire Police said a 54-year-old man was arrested in connection with the incident and was in custody.
A man in a Superman costume saved the day when he stopped a woman being robbed as she used a cash machine.