"This transition won't be easy but I'm looking forward to every second of it with my amazing family," the big-serving 2.08-metre tall American posted on social media alongside a photo showing Isner, his wife and their four children.
"Time to lace 'em up one last time," the 38-year-old Isner said, referring to the year's last major tournament, which starts in New York on Monday.
Isner reached a career-best ranking of world No.8 in 2018, shortly after reaching the semi-finals at Wimbledon, won 16 singles titles and has hit more than 14,000 aces, an ATP Tour record.
That includes 113 - the most ever in a match - in his epic win against Nicolas Mahut that lasted 11 hours, five minutes across parts of three days in the first round at the All England Club in 2010 and ended at 70-68 in the fifth set.
There is now a plaque commemorating that contest on the wall outside Court 18, where it was played.
"Especially once the match got past, you know, 25-all, I wasn't really thinking," Isner said back in 2010.
"Hitting a serve and trying to hit a forehand winner is the only thing I was doing.
That match and Isner's loss to Kevin Anderson by a 26-24 score in the fifth set in the semi-finals at Wimbledon eight years later were a big part of the impetus for the sport's eventual switch to standardising tiebreakers in the decisive sets at all grand slam tournaments.
He was born in North Carolina and played tennis at the University of Georgia, helping the school win the 2007 NCAA team tennis championship, before turning pro that year.
Isner won more than $US22 million ($A34 million) in prize money and for years was the highest-ranked American man.
He has gone just 8-13 in 2023 and his ATP ranking dropped to No.158 this week.
Isner bowed out in the first round at each of this season's first three grand slam tournaments. The last time he got to the third round at a major was at Wimbledon last year, when he defeated Andy Murray at Centre Court.
"It's no secret that I am most definitely not a better tennis player than Andy Murray. I might have been just a little bit better than him today. It was an incredible honour to play him on this court, in front of this crowd," Isner said that day.
"At the age I'm at now, I need to relish these moments. This was one of the biggest wins of my career."
