Djokovic is in his 311th week in the top spot, one more than Federer has spent there.
“Big day today,” Djokovic tweeted Monday.
The 33-year-old from Serbia first reached No. 1 on July 4, 2011, a day after he won Wimbledon for the first time by beating top-ranked Rafael Nadal in the final. Djokovic's ascent represented the first time in nearly 7 1/2 years that a man other than Federer or Nadal was No. 1.
“Any athlete in the world dreams of being No. 1 of the world. This is something that gives us a lot of motivation,” Djokovic said back then, when the ATP marked the occasion by presenting him with a cake shaped like the numeral “1" in the red, blue and white colors of Serbia's flag. “So finally, when you really do it, and when you know that you’re the best, it’s just an amazing achievement.”
Djokovic has gone on to win five titles at the All England Club, along with nine at the Australian Open, three at the U.S. Open and one at the French Open.
His total of 18 Grand Slam singles trophies trails only the 20 claimed by Federer and Nadal for the men's mark.
Djokovic has had five separate stays at No. 1 and finished six seasons there, tying Pete Sampras for the most.
Sampras held the total weeks record of 286 until Federer surpassed him in July 2012. Ivan Lendl stands fourth with 270, and Jimmy Connors is next at 268.
The ATP introduced its computer rankings in 1973.
Djokovic's championship at Melbourne Park last month assured him of staying No. 1 at least until this week and claiming sole possession of the record from Federer.
Djokovic called reaching that milestone a “relief” and said it would allow him to “focus all my attention on Slams, mostly.”
“When you are going for No. 1 rankings, you kind of have to be playing the entire season, and you have to be playing well; you have to play all the tournaments,” Djokovic said. “My goals will adapt and will shift a little bit.”
Federer most recently spent at week at No. 1 in June 2018. He was 36 at the time and that allows him to still hold the record for oldest man to hold that top place.
His 40th birthday is Aug. 8.
After two operations on his right knee in 2020, Federer has gone more than a year without competing. He is scheduled to return to tour action at the Qatar Open on Wednesday.
With so much inactivity, Federer slipped to No. 6 in Monday's rankings, swapping spots with Stefanos Tsitsipas.