The six-times Olympic gold medallist has invested in the company and will act as an adviser on products and services.
The news comes hot on the heels of plans to extend the gym chain’s reach into the South with the purchase of LA Fitness, cementing its position as the UK’s largest gym operator.
Leeds-based Pure Gym, which is buying its rival for between £60m and £80m, intends to convert the 43 LA Fitness clubs into Pure Gym clubs, dependent on regulatory approval.
The chain launched its first branch in 2009 and now has around 530,000 members nationwide.
Sir Chris said: “I have followed Pure Gym’s swift expansion over the past few years and have admired the way in which they have changed the gym market for the benefit of consumers of all ages, abilities and interests.
“I am particularly interested by the fact that 30 per cent of our customers have never been members of a gym before. A business that is encouraging more people across the whole social spectrum to exercise more regularly is a business that I will be proud to be a part of.”
Pure Gym’s chief executive Humphrey Cobbold said: “Chris is a truly outstanding sportsman and a superb technician in terms of training expertise. As a multi-Olympic medal winner he is well placed to advise on strengthening our product offering and services.
“I also know that he is not just interested in elite sports but is deeply committed to helping people of both sexes and all abilities be healthier and more active. I therefore cannot think of a better person to join us and to support our mission of opening up access to affordable, high-quality fitness facilities to as many people in Britain as possible.”
Earlier this week Mr Roberts was crowned North of England EY Entrepreneur of the Year.
Speaking about the LA Fitness announcement, he said: “This deal will allow Southerners to get much better value for money. We always said we should be 50 per cent of the cost of mid market rivals. Southerners can expect their bills to be cut in half.”
Mr Roberts said that existing LA Fitness members will get the benefit of the most up to date kit.
“We will invest on average £1.2m in each gym and we’ll convert all of them,” said Mr Roberts.
LA Fitness is particularly strong in London and the South East.
“This opportunity has allowed us to fill in some gaps in the South,” said Mr Roberts.
The deal will increase the number of Pure Gym sites from 98 to more than 130 - after accounting for the possibility that a handful may have to be sold following scrutiny by competition authorities.