Travelopia’s portfolio of 53 brands covers sailing adventures, tailor-made holidays, sports tours, school expeditions, private jet travel and polar expedition cruises.
It has an international customer base of more than 800,000 travellers each year, and serves more than 70 destinations globally.
Will Waggott, chief executive of Travelopia, said: “KKR’s experience in the sector, global reach and digital expertise make it the perfect partner for Travelopia as we continue to grow.
“We look forward to working closely with the KKR team to continue to develop the business and our customer offer.”
All regulatory approvals required have been granted by the relevant authorities.
Tui said in a statement that it "consistently continues its transformation to an integrated tourism group with main focus on hotel and cruise businesses".
Travelopia was previously part of Specialist Group. It had been managed as an independent unit since the merger of Tui AG and Tui Travel PLC at the end of 2014.