Jane Ellison and Justine Greening joined staff and customers to mark the official opening on Thursday, July 24.
Public health minister, Ms Ellison, got behind the counter and served the Secretary of State for International Development, Ms Greening, with some foreign currency.
Ms Ellison said: "This is a great new service for people in both my constituency and Justine's.
"We're very supportive of this move and are pleased to be able to share this special day with both the Wandsworth Post Office team and its customers."
Ms Greening added: "This brighter, more modern Post Office will give them the perfect platform to provide important services for the surrounding communities now and into the future."
The branch has two entrances, one on the High Street and one backing onto Ram Street.
Improved accessibility has been built in with automatic doors, and a low-level writing desk and space for wheelchair users.
The Wandsworth Crown Post Office opens from 8.30am-6pm on Mondays and Tuesdays and 9am-5.30pm Wednesday to Saturday.