An annual search for the best places to work by jobs website Glassdoor also named charity Oxfam and London Underground in the top 10.
Other firms highlighted included recruitment firm Hays, advertising company AKQA, industrial group GE and retailer Schuh.
"Being named as Glassdoor UK's Best Place to Work for 2016 is a true honour, particularly because this distinction is based solely on feedback from our employees," said Gary Morrison, senior vice president of Expedia Retail.
"The fact that we moved from 25th to first on Glassdoor's list in a single year is a major achievement. Our employees are passionate about travel and are relentless in finding innovative ways to improve our customers' experience. This recognition is a testament to them."
Nick Brown, managing director of London Underground, said: "It's fantastic that London Underground has been named one of the best places to work in the Glassdoor 2016 list.
"We have some of the most talented and dedicated people working for us from all around the world and the contribution that they make every day to keep this city working is second to none. This recognition is a great testimony to everyone working at London Underground that together they are making a real difference to Londoners."
The list of best companies to work in the UK is:
2 Hays plc
5 Schuh Limited
7 ARM Holdings
10 London Underground
14 Amec Foster Wheeler
15 Royal Dutch Shell
16 John Lewis
17 J.P. Morgan
18 Cisco Systems
19 Goldman Sachs
20 Credit Suisse
23 Procter & Gamble
24 Kantar Worldpanel