Allegra will sit on the seventh floor of property developer Harry Handelsman’s Manhattan Loft Gardens development in Stratford, and feature a terrace and garden overlooking the London skyline.
It will also contain a Scandinavian stone bar and walk-in wine room.
Powell’s menu is to focus on modern European cuisine, with the chef sourcing a large proportion of ingredients from farmland in Kent that is owned by Handelsman.
Dishes will include fresh ricotta served with red pepper, charred & salted courgette, rape seed & lemon thyme; smoked eel and confit potato pithivier with parsley sauce; roast chicken with wild garlic sausage, white asparagus and confit garlic cream; and baked apple mille feuille with caramelised honey ice cream.
Powell has previously worked in Dublin's Michelin-star L'Ecrivain under the eye of Irish chef Derry Clarke, and at Wild Honey with Anthony Demtre.
As well as Allegra, Manhattern Loft Gardens will house Stratford Brasserie, overseen by former Soho House chef Ben Harrington. It will also feature lounge bar concept The Mezzanine.
Handelsman acquired the site for the Manhattan Loft Gardens development in 2009. According to Wallpaper magazine, the entire 42-storey project has cost around £300m.