The food-on-the-go business – which has 17 stores here – is taking one of the new food units being developed at the centre on the Saintfield Road.
It will join other food businesses at a new food court being developed, alongside US chicken chain Popeyes.
Greggs has expanded considerably since the Belfast Telegraph first revealed the UK-based chain was setting up shop here back in 2016 – at the time eyeing up to 50 locations.
The chain recently received planning permission to open its first drive-thru in Northern Ireland.
The latest Greggs store here will be located in Co Armagh’s Marlborough Retail Park in Craigavon.
The fast food outlet’s proposal for the drive-thru was recommended for approval by Armagh, Banbridge and Craigavon (ABC) Borough Council – the last stage before official approval.
Greggs has almost 2,500 outlets across the UK.
It opened its first store at the Applegreen service station on the M2 in April 2015.
Last year, Greggs unveiled expansion plans, which included trialling a new 24-hour drive-thru, following a record high for sales.
It will now join new food and drink retailers at Forestside, following the centre’s acquisition by developer and entrepreneur Michael Herbert last year.
Speaking after news of the deal was revealed, Mr Herbert said he had plans to make it into “a food village”.
He said he had plans to make Forestside “more of a leisure destination and a shopping destination.”
It will provide 50 construction jobs and 100 full-time jobs.
US coffee chain Starbucks also looks set to open at the popular shopping centre.
The brand is taking on a unit at Lesley Forestside, and will join cafes such as Caffe Nero and Jamaica Blue.
It appears to be taking a unit outside the main building itself, close to the roundabout and entrance of the centre on the Upper Galwally side.
Meanwhile, fried chicken brand Popeyes will open its first restaurant in Northern Ireland at Forestside on September 20.
The chain said the restaurant will open its doors at 11am and have also revealed the first three people in the queue on that day are in line to win free chicken sandwiches for a year.
The first 50 customers in the queue will win a free chicken sandwich alongside other merchandise.
Popeyes says it intends to open more than 30 new restaurants and 2,000 new jobs around the UK.
It said it has a goal of opening 350 UK restaurants over the next 10 years, after rapid growth in continental Europe in recent years.
It’s also thought peri peri chicken giant Nando’s looks set to open its latest restaurant here at Forestside.
The South African-owned firm will take one of the newly-constructed units at the centre, just off the Saintfield Road, according to new plans.