The site, which launches in March and will be found at will expand the range of theatre choices and content compared with lastminute's present theatre offering.
There will also be a newsletter targeted at regular customers and potential new theatregoers.
Paul Shaw, head of lifestyle at Lastminute.com, said: "Together Lastminute.com and Theatrenow are using their collective experience to create a strong new theatre ticketing channel. Theatrenow's history of providing discount and last-minute theatre tickets makes it an ideal partner and a great fit with the Lastminute.com brand."
The service will initially offer tickets to theatres in the West End and greater London only, but the service is expected to roll out across the UK later this year.
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