Canelo will take a step down in weight to super middleweight to defend his undisputed status as WBC, WBA, IBF and WBO champion at 168lbs.
The Mexican was defeated on points this month by light heavyweight Russian Dmitry Bivol – his first taste of defeat in nine years.
Canelo has now decided to end his bitter rivalry with GGG rather than activate his rematch clause with Bivol.
Golovkin, the WBA and IBF middleweight champion, will move up a division to face Canelo.
The pair first met in the ring in 2017. The fight ended in a controversial split draw with many feeling Golovkin should have been declared the winner.
Canelo took the spoils in the subsequent rematch with a narrow points victory.
The third instalment of the trilogy is expected to take place in Las Vegas, the same venue as the two previous fights.
“These are two men that bitterly dislike each other and want to end this incredible series with a blistering KO.
“I truly believe this will be the most thrilling fight between these two great champions and it will be fireworks from the first bell to the last man standing.”
Can Canelo overcome GGG’s titanium chin?
The biggest highlight from the two previous fights came in the initial fight between the competitors.
In the ninth round, Canelo connected with a big power-punch, catching an advancing GGG flush on the chin.
However, GGG brushed the punch off like it was nothing and continued to advance on a shocked Canelo.
One user wrote: “Khan got knocked out just from watching this on his TV,” while another said: “I can feel my ears beeping and my chin going numb just from watching.”
Another nailed it by simply saying: “It was then that Canelo audibly said “by decision it is then…” lmao.”
Canelo will be hoping to get back to winning ways and inflict only GGG’s second defeat.
Forty-year-old Golovkin comes into the fight having won his four matches since that sole career defeat to Canelo.
He added: “I hope to see you on September 17.”