Pimlico Plumbers has been sold to US home services group Neighborly.
The deal will see founder Charlie Mullins offload his 90% stake in the group and is expected to be worth between £125m and £145m, according to the Financial Times.
The entrepreneur's son, Scott Mullins, will retain a stake of about 10%, and continue his role as chief executive.
The London-based firm currently makes nearly $70m (£50.7m) in revenue a year, and employs more than 400 workers.
Founded in 1979, Pimlico's services include heating, plumbing, bathrooms, drainage and electrics. It completes an average of more than 100,000 service jobs for central London homeowners and businesses each year.
From starting the plumbing business with a second-hand van and a box of tools, Mullins said he had received approaches from a number of buyers after hiring advisers from Cavendish Corporate Finance.
"We had various people who wanted to buy the business, and interest from all over the world, including France, America, and somewhere in the Middle East," Mullins told the BBC.
The businessman often speaks publicly on economic matters and was an opponent of Brexit.
He said the firm had experienced a strong year despite the coronavirus pandemic, with both in and out-of-hours calls increasing, as well as emergency call outs.
"Covid helped to lift the company to another level," he said, pointing to an increase to 2,000 to 3,000 jobs a week. "It now needs to go international."
He added: "The business will always be something I will cherish. It has been a lifetime of work, and what it has achieved is remarkable. Neighborly will take that to the next level."
Mr Mullins plans to use some of the income from the sale to back other ventures in music promotion and overseas property.
Neighborly, founded in 1981, is a home services provider, serving more than 10 million residential and commercial customers. As well as plumbing, it provides pest control, cleaning, and home inspection services.
The acquisition allows Neighborly to extend its international reach. Neighborly was bought by KKR from investment firm Harvest Partners just two months ago.
Mike Bidwell, president of Neighborly, said: "We are thrilled to be growing our global footprint with the addition of Pimlico as the next subsidiary brand to join our global family of home service professionals.
"Pimlico's wide array of trade services as well as its exceptional customer care perfectly align with Neighborly's purpose, which is to build an extensive service community known for providing excellent experiences."