Bosses at the chain announced a pre-tax loss of £13.7 million in 2020, compared with a £108.3 million profit a year earlier, with sales dropping from £1.17 billion to £811.3 million as stores closed their doors for large swathes of the year.
But the company said it remains positive for the future and has committed to opening 100 new stores this year.
Delivery services and a partnership with Just Eat helped offset some of the falls, the company said, with 9.6% of total sales in the first ten weeks of 2021 now coming via deliveries.
But the latest lockdowns and restrictions since the start of the year have hit overall sales, the company said, with like-for-like sales down 28.8% in the ten weeks to March 13.
Stores have remained open for takeaways, as they are classed as essential retailers, however city centre locations and travel hub sites have seen substantial falls due to the stay-at-home Government orders.
Excluding sales in Scotland, where stores have been closed to walk-in customers for the majority of the year, like-for-like sales were down 22.4% during the period.
The company said the results for 2020 were slightly better than expected, considering the lockdowns, adding that it benefited from the furlough scheme and business rates holiday.
Bosses added they have access to a new £100 million revolving credit facility to fund further expansion beyond the 2,078 stores in operation.
Greggs listed on the London Stock Exchange in 1984 and had never previously reported a loss since becoming a public company.