The Wolverhampton-based company said it is opening about 70 per cent of its 1,000 managed and franchised pubs in England.
This includes 93 in the Express and Star circulation area and 28 in the Shropshire Star circulation area.
From Monday, Government rules will allow pubs and restaurants to reopen to serve customers in beer gardens or other outdoor serving areas.
It follows months of complete shutdown for the sector.
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Marston's said it will reopen the 700 pubs in England "on or around" April 12 and Scottish and Welsh pubs will open on April 26, subject to final confirmation from the authorities.
The 700 pubs represent a large majority of the company's pubs that have beer gardens or other outdoor serving areas.
A week ago, the business revealed it had carried out work at around 300 pubs to ensure their outdoor serving areas are able to safely host guests.
The company's operations director Ed Hancock said: "There is no 'one size fits all', we have to think about how the space will be used and most importantly what guests are looking for.
"Moving through 2021 and beyond, external spaces will become even more valuable and the industry needs to continue to provide a safe, comfortable environment for guests."
Marston's said the remainder of its managed estate in England should open with restricted indoor trading around May 17, as long as the Government sticks to its plans.
The chain is assuming that normal tradition conditions will return on June 21.
The company also confirmed to investors that it has managed to secure financial waivers for several of its funding sources up until the beginning of next year.
This will buy the pub giant some time as it tries to restart operations after what may be the toughest year in history for the hospitality industry.
It will announce interim financial results on May 19.