In nearly 20 years in post the 61-year-old has overseen 29 trophy wins including 13 league titles, four domestic trebles, and participation in the knockout stages of the UEFA Champions League on three occasions.
Supporters of Celtic and other clubs were quick to react to the news.
Evan McFarlane tweeted: "Lawwell is absolutely going to end up at the SFA, isn’t he? 4D Chess."
Matt McGlone wrote: "The big question now is who calls the shots and makes crucial future decisions for the club over next five months? Hard for Dominic McKay to interview any new manager whilst still in his current job!"
Lewis Laird reacted: "Looking at it, in terms of our finances Peter Lawwell did a good job. But overall, it’s definitely time to move on. Far too high a wage and realistically was acting like a DOF a lot of the time. Going from here, the rebuild has to start. Move forward to become a modern club."
Rangers fan Gavin Wilson joked: "Peter Lawwell running away. Celtic selling their best youngster. Beating Hibs. Morelos stamp. Red Arrows. Michael Stone is home for 55. What a week for us Rangers fans."
Chris Buckley tweeted: "Some might disagree but Lawwell leaving could end up being one of the worst things to happen."
Sam Smith said: "Great news Lawwell has retired. Just need rid of Lennon now and we can start to move forward. Lawwell did a decent job most of the time and guided us through one of the most successful periods in our history, but he also made some monumental mistakes."
Sean McBride offered a different side of the departing CEO: "Peter Lawwell was brilliant with our family when my grandpa passed away. A top man."
Dean McLean added: "Mr Lawwell, thanks for the memories. You’ve presided over a successful reign and put the club on a strong financial footing. Looking forward to the change of direction in the summer."
Hugh McGuigan predicted: "As with Fergus McCann, many won't properly appreciate Lawwell until he's long gone."
Simon Houston wrote: "Any Celtic fan who doesn’t think an enormous debt of gratitude is owed to Peter Lawwell needs their head examined. I hope it’s not the case that we don’t know what we’ve got ‘til it’s gone."
Joe Mulholland tweeted: "Just can't understand Celtic fans. A treble x treble of trophies, 9 in a row and a cup this season already under Lawwell and Lennon. I remember the barren years at Parkhead and they were difficult times so be careful what you wish for."
Fergus Boden said: "Overly simple take: Appointing Chief Operating Officer of SRU is an interesting call though. Clearly the club see the role as largely commercial, which contrasts with fans giving Lawwell a lot of stick for matters more related to what happens on the pitch."
Andy Hynes summed up: "Peter Lawwell going... overall he's been outstanding business-wise; of course he's made two or three really expensive mistakes like [John] McGinn, falling out with [Brendan] Rodgers, and Neil Lennon's second stint at the job."