TravelUp was ranked 37th in the list after growing turnover 75% over the past three years to £77.3 million.
Gross sales, said the company, grew to £313 million in the year to March 2018. The OTA now employs 74 people and holds an Atol for 110,000 passengers.
It also grew its web traffic to 20,000 hits a day in the year to March 2018, up 65% on the previous 12 months.
TravelUp was founded in 2004 by Pakistani business travel agent Ali Shah, who came to the UK with no experience of the UK travel market.
It now offers flight-only and package deals online through its TravelUp, Holiday Genie and Bravo Travel brands.
“We have worked so hard over the past 14 years and I would like to thank all of our team both past and present for their hard work and dedication that has made TravelUp what it is today,” said Shah.
Reading-based HalalBooking.com, meanwhile, was ranked 26th after growing its sales 90% in the year to December 2017 to £10.1 million on a staff base of 36.
The Fast Track 100 ranks Britain’s private companies with the fastest-growing sales.
It has also tipped two other travel companies for success over the coming years.
Firstly, it has identified “lifestyle content platform” Culture Trip as a likely disruptor, its content produced by more than 300 freelancers now attracting more than 18 million views a month.
It uses AI and algorithms to target its content at millennials.
The other is holiday cottage rental specialist Sykes Holiday Cottages, which is aiming to grow its business to 2.5 million holidaymakers by 2020.
Sykes attracted more than £50 million investment from private equity firm Livingbridge in 2014.