The highly successful border counties supermarket will bring new outlets to the towns.
The announcement was met with enthusiasm by both mayors.
"It sounds just the ticket and I'm very pleased for both Coleford and Lydney. Anything that keeps jobs in the towns is to be welcomed and from what I hear they will make a useful contribution to the facilities," said Coleford's mayor, Sue Merrikin.
Her views were echoed by Lydney's Terry Glastonbury who described the news as a shot in the arm for the town.
"When you look at the bigger picture, you have to say Lydney is very lucky. There are only a couple of empty shops and my hope is that the arrival of Harry Tuffins will add even greater footfall to the benefit of everyone," he said.
The Somerfield stores, owned by the Co-op, had to be sold as part of the take-over deal.
Both stores will open as Harry Tuffins outlets early in February. Lydney will be the biggest with 11,000 square feet of floor space. Coleford's offers 5,000 square feet.
Company managing director Paul Delves, operations manager Richard Whittall and general manager Mark Williams were present at both Lydney and Coleford to meet and chat with staff when the announcements were made.
In a statement they said both Lydney and Coleford would be included in the NISA group, a powerful buying consortium. In addition both stores intended to expand non food products and offer a greater and more comprehensive range.
Harry Tuffins says they will continue with their policy of supporting local producers.
Operations manager Mr Whittall said the Lydney store would open on February 4 and Coleford a week later.
"They are excellent outlets in nice towns and with good people and we are very much looking forward to the moves. We have talked to the staff – 77 in all – and all those jobs are secure. If things go well there could be some additional jobs," he said.
Mr Whittall said the news of the take-overs had been met with a postive response.
"For the staff it will end 14 months of uncertainty and it is obviously a big relief for them," he said.
The company was founded by Harry and Doris Tuffins in 1955 with two petrol pumps and a garage. After a short while they added a shop.
Now there are seven major outlets: Churchstoke, Bishops Castle, Knighton, Craven Arms, Ludlow, Cleobury Mortimer and Machynlleth.