The trade union will be one of the first to use the venue, which is set to open May 2019.
Its congress, taking place the following June (2020), is expected to attract more than 1,000 delegates over five days.
The union, which supports more than 600,000 members from across the UK and Europe, has also revealed that it plans to use the proposed new hotel at The Sands Venue on Central Promenade as its conference base.
Tim Roache, GMB general secretary, said: "We're absolutely delighted to be back in Blackpool in 2020 and looking forward to trying out the impressive new facilities.
"The GMB has spent many happy times in Blackpool over the years, so we're really looking forward to bringing our congress to the Fylde Coast once again.
"Around 1,000 delegates, visitors, exhibitors and staff - as well as the nation's press and TV - will be able to enjoy Blackpool's wonderful hospitality during our five day event."
Councilor Simon Blackburn, leader of Blackpool Council, said: "This is fantastic news for Blackpool, we are delighted that the GMB have chosen to host their annual congress in the resort, and I look forward to welcoming them here. The Trade Union movement have been great supporters of Blackpool over decades, and I'm sure this will be the first of many Union conferences heading our way.
This is the first national conference to be confirmed in our new, state-of-the-art conference centre, and I am delighted that the GMB, recognising our investment, now feel the time is right to enjoy a return to the seaside.
"This demonstrates the real and growing confidence in the Blackpool offer and demonstrates that what we are doing here, is what organisers are looking for.
"With ongoing investment into the resort’s accommodation offer, there has certainly never been a better time for conference organisers to consider Blackpool for their upcoming meetings and events in the future.
"The conference will bring a further welcome boost to the local economy, helping us to attract new organisers to the resort in the future."