The 1,500 sq ft bar will open later this year at 78 Queen Victoria Street and serve until 1am. Nightcap co-founder and former Dragon's Den star, Sarah Willingham, said: "Since the lifting of the Covid restrictions we have been impressed with the strong trading at all of our City sites in London.
The AIM-listed chain, which operates premium bars across London, Bristol and Birmingham and recently took over the Adventure Bar Group, said it is also in various stages of negotiations over opening five more sites around the UK.
It comes as Mayor Sadiq Khan urges businesses to highlight the fun of after-work socialising to help draw staff back to the capital's offices.
The Let's Do London Lates season includes late-night jazz and cabaret in the crypt of St Martin-in-the-Fields and a collaboration between the English National Opera and Fabric nightclub. There are also new "After Work Social" roundels in several Tube stations.
Meanwhile the City of London Corporation has told the Square Mile it must evolve to the new hybrid-working ecosystem.
Nighcap shares rose 1.25% on the update on Monday morning.