The move will give the Leeds-headquartered business significant scale in Europe and rapidly accelerate its international expansion, which includes plans for trial sites in the USA, it said.
The low cost gym brand has opened over 70 sites since being acquired by funds controlled by Leonard Green & Partners (LGP) in 2017 and will be trading from 263 locations in the UK by the end of this year.
Further expansion in the UK is planned for 2020 and beyond. Backed by LGP, international expansion has also been a strategic focus in order to diversify, gain scale advantages and access to additional opportunities for growth.
Fitness World has 240 gyms across Denmark, Switzerland and Poland with a total of 600,000 members.
The combined group will be trading from over 500 sites and in that regard will be second only to Basic Fit in the European market.
Humphrey Cobbold, chief executive of PureGym, said: “This transaction brings together two well matched, successful market-leading businesses and the combination creates a powerful platform from which to accelerate growth and deliver on our purpose of getting even more people, more active, more often.
“The acquisition of Fitness World is a transformational deal for PureGym and will support our long-held ambition to become a leading international gym and fitness operator.
Fitness World is a business we know well and have long admired.
“The team there have done an outstanding job in building unparalleled leadership in the highly attractive Danish market with exciting growth positions in Switzerland and Poland.”
Steen Albrechtslund, chief executive of Fitness World, added: “I am delighted to be partnering with PureGym, a company that has, in just 10 years, fundamentally changed fitness provision in the UK.
“Their decision to invest in Fitness World is testament to the business we have built, which is the overwhelming market leader in Denmark and a growing player in Switzerland and Poland.
“Like PureGym we are passionate about making fitness more affordable and accessible.”
The transaction is expected to be completed in early 2020