Worldpay has agreed a £9.3 billion merger deal with US rival Vantiv in a tie-up that will create a global payments processing giant with a combined value of £22.2 billion.
The deal, which comes after a second extension to the talk deadlines on Tuesday, will see Vantiv pay 397p a share for Worldpay, or £8 billion, plus £1.3 billion to cover debts.
The combined group will be called Worldpay and will be led by Vantiv's Charles Drucker as executive chairman and co-chief executive, with Worldpay's current boss Philip Jansen as co-chief executive.
Mr Drucker said: "This is a powerful combination that is strategically compelling for both companies.
"It joins two highly complementary businesses, and will allow us to achieve even more together than either organisation could accomplish on its own."
Under the terms of the deal, Worldpay shareholders will own 43% of the company, with 57% held by investors of Cincinnati-based Vantiv.
The combined group will have a secondary listing on the London stock market, but will have its primary listing in New York.
Cincinnati, Ohio, will become the group's global and corporate headquarters, while its international HQ will be in London.
Mr Jansen said: "The growth of eCommerce and the way consumers expect to transact is increasing complexity for businesses around the world.
"Our unique combination of scale, innovation, technology and global presence will mean that we can offer more payment solutions to businesses, whether large or small, global or local, enabling them to meet consumers' increasing demands and helping them prosper."
The two firms will look to cut around 200 million US dollars (£154 million) from costs after merging.
Vantiv confirmed it has "high regard for the skills and experience" of Worldpay's management and 5,000-strong workforce and their existing employment and pension rights will be "observed".
The combined group will process around 1.5 trillion US dollars (£1.2 trillion) of payments and 40 billion transactions through more than 300 payment methods in 146 countries and 126 currencies.
Worldpay processes millions of payments a day in stores, online and on mobile phones.
It was owned by Royal Bank of Scotland until the state-backed lender sold off its remaining stake to private equity firms Advent International and Bain Capital in 2013.
The company later sealed the biggest flotation of 2015 when it listed on the London Stock Exchange with a valuation of £4.8 billion.
Vantiv handled 25 billion transactions worth 920 billion US dollars (£711 billion) last year.
It is largely focused on the US, helping merchants, banks and credit unions accept card payments, as well as gift cards and online payments.