The Financial Services Compensation Scheme has awarded a contract to Capita to provide its claims handling service.
This contract, which will begin in July 2018, will consolidate all of the FSCS's claims handling and customer services for the next four and three-quarter years, with an option to extend it for up to two years.
Jimmy Barber, the FSCS's chief operating officer said: "Our decision to consolidate our claims handling services in the new partnership will help ensure that customers are provided with an outstanding experience when making a claim.
"It underpins our work to transform the customer experience, through investment in technology and digital development, and adds improved resilience through scale."
Previously the FSCS has outsourced the handling of most of its complaints to a number of different companies.
But earlier this year the FSCS's chief executive Mark Neale said it would move to a single company would allow it to improve efficiency and customer service because that company would have a much greater incentive to invest in claims handling process.
In January Capita's share price fell more than 40 per cent after the company after it issued a profit warning and suspended its dividend.
The company's new chief executive has said he has begun a "transformation programme" to make Capita less complex, less driven by short-term focus and give it more "operational discipline".
Capita, which employs 69,000 staff providing back-office and IT services for government departments, local authorities, and banks, first ran into trouble in 2016 when it announced a series of problem contracts, including a botched IT overhaul for the London congestion charge, that wiped nearly £2bn off its market value in one day.
More profit warnings followed and the company ousted its chief executive Andy Parker and dropped out of the FTSE 100 last year.