CAB Payments Holdings Ltd has set an offer price of 335p per share for its initial public offering (IPO), which will give it a debut market cap of £851.4mln.
Analysts previously estimated that the provider of corporate cross-border payments and foreign exchange services, could achieve a valuation of between £0.8bn and £1bn.
The offer is expected to take place later on Wednesday, it said, which involved private equity backer Helios Investors selling down its stake.
Chief executive Bhairav Trivedi said he felt the offer price was "compelling" and the Sutton-based company has been "pleased with the investor engagement so far and are excited to continue to meet the institutional and retail investment community over the next week".