Neil Woodford-backed Ratesetter has become the last of the big peer-to-peer lenders to be given the green light by the City watchdog.
Rival lenders Zopa and Funding Circle were granted full authorisation as a P2P lender by the Financial Conduct Authority earlier this year after several years of waiting.
"Authorisation has been a long but positive journey during which we have learnt a lot, improved our infrastructure and implemented important changes, notably making the business more transparent," said chief executive and founder Rhydian Lewis.
He added: "Authorisation is a milestone but not an end in itself and we look forward to working with the regulator and all stakeholders to continue to deliver good customer outcomes and to grow RateSetter.”
Read more: London P2P startup Lendable lands £100m
The alternative finance platform has lent £2bn since launching in 2010.
The FCA first announced plans to regulate P2P activity in 2014, taking over from the Office of Fair Trading which oversees consumer credit. They have had interim permission since then.