Last month, Lidl said it would introduce a living wage of £8.20 an hour, or £9.35 an hour in London.
But Northern Ireland staff were not included at the time, with Lidl saying this was due to the way its business was organised.
Lidl has now reversed that position.
The company added that a similar pay commitment is being made to staff in the Republic of Ireland.
Susan Fitzgerald, a regional officer with the Unite union, welcomed the company's decision.
"This is a very significant victory for Lidl workers, our members and Unite, who led the campaign to demand equal pay for workers in Northern Ireland," she said.
"We are particularly pleased that Lidl's adoption of the living wage will extend to their workforce in the Republic of Ireland.
"This announcement means other retail chains are now on notice that they need to pay the living wage - there can be no justification for poverty-pay."
Earlier this year, the government announced there would be a new, compulsory National Living Wage of £7.20 an hour from April 2016.
But that figure is lower than the £8.20 recommendation set by the independent Living Wage Foundation.
It is the rate calculated by academics as the level of pay that will give workers enough for a basic standard of living.
It is an informal benchmark, not a legally enforceable minimum level of pay.
Lidl has received plaudits for becoming the first UK supermarket to implement the independently recommended living wage.
But its position in Northern Ireland became a PR disaster with some consumers threatening a boycott and trade unions planning protests outside shops.
John Paul Scally, the managing director for Lidl in Ireland, said the majority of staff already earn above the living wage.
"It is important for us to ensure that those whose hourly pay falls below £8.20 benefit from a substantial increase," he said.
"This would bring them to a level that is more reflective of enjoying a better standard of living."
Lidl staff at store assistant level in Northern Ireland currently start at a basic £7.20 an hour.
Now all store assistants will earn a minimum of £8.20, rising to £8.80 an hour incrementally within three years.
Mr Scally said the move will require an investment but he wanted to reassure customers that it will not lead to price increases.
Lidl has about 600 employees in Northern Ireland who work at 38 stores and a distribution depot.

Lisa Passey and Wayne Dale left son Kian Dale in an upstairs bath seat for at least 13 minutes, Worcester Crown Court was told.
Ms Passey was with a friend downstairs and Mr Dale was "socialising" and using his computer".
Ms Passey, 28, and Mr Dale, 45, both deny gross negligence manslaughter
See more stories from across Herefordshire and Worcestershire here
Opening the prosecution, Jonas Hankin QC, said: "When, finally, Wayne Dale went upstairs to the bathroom, baby Kian had drowned."
Mr Hankin said that family friend Jeanette Morgan had visited the then-couple's home in Kyreside, Tenbury Wells, Worcestershire, on 26 September 2015.
She and Ms Passey "drank coffee together and smoked cigarettes" in the sun on the patio, before Mr Dale joined them, he said.
Mr Hankin added: "She asked him to burn a copy of the UB40 album, playing in the kitchen, which he did."
After Kian was discovered lifeless in the water, Ms Passey dialled 999 telling the operator her baby had "drowned in the bath", the court heard.
The court heard Mr Dale, of no fixed address, told police officers he "had a beer, rolled a cigarette outside and burned a CD" and that he had only left his son for "a couple of minutes".
A post-mortem examination found the child's death was consistent with drowning, including what was believed to be soap bubbles in his lungs.
Ms Passey, of Tenbury Wells, initially claimed she had not run a bath, but twice changed her account, the prosecutor alleged.
The trial continues.
The supermarket chain Lidl will now include Northern Ireland staff in the pay rise it has awarded to workers in the rest of the UK.
[NEXT_CONCEPT]
A couple left their 13-month-old son alone in a bath where he drowned as they entertained a friend, a court heard.