Profit after tax dived to £100 million ($141 million, 116 million euros) in the six months to the end of March, Compass said in a results statement.
That compared with £586 million in the same part of the prior financial year.
The London-listed firm, whose main rival is Sodexo of France, added that revenues collapsed by almost a third to £8.4 billion.
The deadly Covid-19 pandemic ravaged the food services sector, as lockdowns shuttered schools and company canteens around the world.
The UK government reimposed England’s lockdown in early January, but began lifting restrictions at the start of March with the reopening of schools.
Compass forecast Wednesday a “gradual improvement in revenue” in its third quarter despite a mixed global outlook.
“With the gathering pace of vaccination rollouts across our major markets, we are working closely with our clients to prepare to reopen their sites safely, although the picture across the world remains mixed,” noted chief executive Dominic Blakemore.
Compass added that new business jumped in the reporting period as the pandemic persuaded many companies to outsource their catering needs for the first time.
“Over the last six months … clients sought quality partners with health and safety expertise, supply chain resilience, and financial stability,” said Blakemore.
“As a result, new business wins have increased due to the acceleration of first time outsourcing, which now accounts for about half of our growth.”