The 54-cover restaurant will open at 'pop-up mall' Boxpark on Shoreditch High Street on 20 March and will serve fish from Cornwall.
Simply Fish Shoreditch follows the success of Simply Fish Camden, opened by Chris Singham and executive chef Sherif Hassan last year and will offer diners the same choice - fish, cooking style and sauce with starters priced from £4 and mains priced between £10 and £15.
The restaurant will also offer takeaway and delivery with a team of electric delivery bikes to distribute orders around the Square Mile.
Manager Nico De Sario said: "We wanted to open a restaurant which made fresh fish accessible to a wide range of the Shoreditch crowd and also attract office workers looking for healthy affordable lunch options. The menu offers choice but is unpretentious and unfussy - the quality of the ingredients speak for themselves."