Vital Ingredient, which has 13 remaining restaurants, specialises in made-to-order salads and soups.
Tossed has purchased the chain from privately-owned investment firm FCFM Group Ltd, which bought it out of administration in January this year with the closure of seven London sites.
The combined group will operate 38 locations across the capital, UK Welcome Break service stations and Dubai.
Tossed founder and managing director Vincent McKevitt says the move has created “one of the largest healthy eating groups in the UK”.
“Our companies have different strengths and we are looking forward to taking the best from both,” he says.
“Vital has a great team and superb locations, whilst Tossed is strong in hot food and technology.
“We will look to review our systems and cherry pick the best from both brands.”
Tossed, which aims to show “healthy eating doesn’t have to be boring”, opened its first site in London’s Paddington in 2005.
The now 25-strong group claims to have launched Europe’s first "cashless" restaurant in 2015.