The merger with Apollo Strategic Growth Capital will deliver gross proceeds of up to $1.2 billion, including a $335 million private investment in public equity, or PIPE.
Investors in the PIPE included investment manager Ares Management Corp, travel technology company Sabre Corp and Zoom Video Communications Inc.
The deal comes at a time when business travel is recovering from a pandemic-induced slump, in a boost for companies like AmEx GBT that help plan corporate trips.
AmEx GBT was a wholly-owned unit of American Express Co until 2014, when the payments processor sold half its stake to a consortium led by investment firm Certares LP.
Singapore sovereign wealth fund GIC and the Carlyle Group were looking to purchase a 20% stake in the company in late 2019 but pulled out of the investment in May last year as the COVID-19 crisis hammered the travel sector.
AmEx GBT has over the past year strengthened its business by acquiring several companies, including Ovation Travel Group, Expedia Group's corporate travel arm Egencia and 30SecondsToFly, a travel tech startup that uses artificial intelligence.
The combined company will be renamed Global Business Travel Group after the deal, but it will continue to do business under the AmEx GBT brand name.
The merger is expected to close in the first half of 2022, after which the company will trade on the New York Stock Exchange under the symbol "GBTG."
Special-purpose acquisition companies (SPACs), or blank-check firms, are shell companies that are raised with the intention of merging with a private entity to take it public by sidestepping a traditional initial public offering.
(Reporting by Sohini Podder in Bengaluru; Editing by Aditya Soni)