The fried chicken chain has gradually opened 20 of its sites over the past two weeks for deliveries only.
It said it will now reopen an additional 80 restaurants across the UK this week, taking its total to 100 by Monday.
The chain, which has over 900 sites nationwide and employs around 24,000 people, shut all its restaurants last month due to the coronavirus lockdown.
The raft of reopenings comes as rivals including Burger King and Pret a Manger also push forward in restarting operations for deliveries.
McDonalds said on Tuesday that it is carrying out tests behind closed doors this week in preparation for reopening sites.
KFC said it will serve a "limited menu" to help smaller kitchen teams maintain social distancing, while "stringent processes and hygiene measures" are in place.
Paula MacKenzie, managing director for KFC UK & Ireland, said: "I'm really proud of the way we, with our franchise partners, have been able to carefully get some of our restaurants back open for delivery over the last two weeks.
"This next stage allows us to continue to provide wider access to hot food for those who need it most, whether that's key workers after a long shift or those working from home who need a quick, affordable dinner for the family.
"I'm hugely appreciative of our team members who have returned to work - it's a challenging time for everyone, but we're so glad to play our part in helping to feed the nation."
Food will be delivered through Deliveroo, Just Eat and Uber Eats, it said.
The company also said it will continue to donate meals to the NHS and key workers, committing to deliver 10,000 meals a week in partnership with Deliveroo.
Meanwhile, Burger King said on Wednesday that it hopes to open at least 350 of its restaurants by the end of June as part of a staggered reopening after the lockdown.
It has already announced plans to open 12 restaurants out of its current crop of 500.
Speaking to the BBC's World At One programme, UK chief executive Alasdair Murdoch said: "We would anticipate that by the end of June, we will be getting towards 350 and 400.
"We see that some of the others will be difficult to open - some are in airports.
"At this stage none of us really have the visibility on when they might do."
He said a scaled-back menu would allow staff to socially distance while making the food, with the arrangements being put into place for drive-through restaurants, and with trials set to start on how to reopen high street walk-in locations.