Situated close to Borough Market, The Globe Theatre and Southwark Cathedral, the 90-cover restaurant will be the steak group's ninth permanent location in the capital.
As with its other sites, the focus of the menu will be on the eponymous flat iron steak, although the menu will also serve a range of other cuts including sirloin and rib-eye.
Sides will include beef dripping chips; roast aubergine with tomato and basil; creamed spinach; and crispy bone marrow garlic mash.
Fred Smith, head of beef, and his team will also be debuting a new ex-dairy short rib chilli cheeseburger special, available exclusively at Clink Street for the month of September.
"After the well-publicised challenges of the past 18 months, it feels really exciting to be able to open a new Flat Iron restaurant again," says Smith.
"Clink Street is a historic area of London and we’ve got a beautiful Victorian building to work with. We can’t wait to meet our new neighbours and continue to demonstrate Flat Iron’s commitment to quality, working with the very best suppliers and produce.”
Designed by Macaulay Sinclair, the new restaurant will embrace the building’s Victorian history, balancing it with contemporary finishes.
Original cast iron columns will be exposed and reclaimed Victorian Staffordshire blue quarry tiles laid throughout, providing contrast to the natural tones of the room with light walls, solid oak tables, tan leather banquette seating and warm lighting.
Flat Iron opened its first permanent restaurant site in Soho in 2012.