The former Celtic winger stepped up to convert a 36th minute penalty after Jesse Devers had his heels clipped by Killian Brouder. McCourt coolly stroked the ball past Tommy Holland to delight the majority of the 2,379 in attendance.
Eight minutes into the second half, Nathan Boyle drew a good save from Holland as Harps set about doubling their lead.
Limerick were dealt a blow 19 minutes from the end when goalkeeper Holland was carried off on a stretcher.
It meant both sides were down their first choice 'keepers.
Harps were without Ciaran Gallagher, whose season has been ended by a knee ligament injury. The absence of Gallagher, with 14 clean sheets behind him during Harps’ surge for promotion, left Harps without one of their most experienced men.
Mark Timlin failed a late fitness test and a suspension kept Mark Coyle out.
The injury list certainly rocked Harps and Conor Ellis almost turned an early screw on the home side. After beating Peter Burke - Gallagher’s replacement in goal - in a race for possession, Ellis shot against the post.
Moments earlier, an effort by Limerick skipper Shane Duggan rose just too much, but it was a clear indication of intent from the Shannonsiders - who had just three wins in their last 13 League games.
Devers forced Holland into a save before McCourt put the home side in front and they held on in spite of strong pressure.
This was a repeat of the 2015 play-off between these sides, when BJ Banda netted a late winner in extra time to send Harps into the top flight.
Limerick launched a late bid to draw level and Barry Maguire’s header was cleared off the line by Gareth Harkin.
Derry Pele: Paddy McCourt's career in pictures as Celtic hero approaches retirement [Photos] Close
Paddy McCourt celebrates Finn Harps' promotion back to the top flight after the final match on his playing career.
GLASGOW, SCOTLAND - SEPTEMBER 11: Paddy McCourt of Celtic celebrates after scoring during the Clydesdale Bank Premier League match between Celtic and Hearts at Celtic Park on September 11, 2010 in Glasgow, Scotland. (Photo by Jeff J Mitchell/Getty Images)
Celtic's Paddy McCourt celebrates the opening goal during the Clydesdale Bank Scottish Premier League match at Celtic Park, Glasgow.
Despite his wonderful skills Paddy McCourt failed to secure a regular starting place at Celtic
Paddy McCourt savours scoring for Northern Ireland against the Faroe Islands
Golden night: Paddy McCourt celebrates his brace against the Faroes in August 2011
BELFAST, NORTHERN IRELAND - OCTOBER 11: Paddy McCourt (L) of Northern Ireland competes Frodi Benjaminsen of Faroe Islands (R) during the Euro 2016 Qualifier between Northern Ireland and Faroe Islands at Windsor Park on October 11, 2014 in Belfast, Northern Ireland. (Photo by Charles McQuillan/Getty Images)
BRIGHTON, ENGLAND - OCTOBER 25: Paddy McCourt of Brighton attacks past Jordan Bowery of Rotherham during the Sky Bet Championship match between Brighton & Hove Albion and Rotherham United at The Amex Stadium on October 25, 2014 in Brighton, England. (Photo by Charlie Crowhurst/Getty Images)
Far right is Celtic and Northern Ireland footballer Paddy McCourt among the Foyle Harps team from 1992 Mallusk NI U-11 Tournament Winners? Picture kindly submitted by Liam Quinn
In March 2015, McCourt played for a Derry City Select against a Northern Ireland Select in the Mark Farren Fund Match by Derry boss Kenny Shiels opted against signing the local man, paving the way for his move to Glenavon.
Moving on: Paddy McCourt has struggled to adjust to life with the Lurgan Blues and will weigh up his options
McCourt helped Glenavon win the Charity Shield against Crusaders.
Picture by Jonathan Porter/Press Eye
Paddy McCourt could make his final appearance for Finn Harps tonight.