The 31-year-old was forced to dig deep to reach his triple century, coming back from the brink of defeat to beat Davis Cup team-mate Stanislas Wawrinka on Thursday to make the quarter-finals of the Shanghai Masters.
For a long time it appeared that Federer, overtaken by younger rivals Rafael Nadal and Novak Djokovic, would never return to top spot -- leaving him agonizingly short of Pete Sampras's record of total weeks at number one.
Used to regularly picking up Grand Slam wins, Federer went nine majors without a title, fuelling speculation he was a fading force.
But his Wimbledon triumph this year pulled him level with the American great on a record seven titles at the All England Club and catapulted him back to the top of the rankings. A week later he overtook Sampras's mark of 286 weeks.
"It's obviously an amazing number. I never thought of something like this when I was a little kid, that's for sure," said a relieved Federer after his narrow escape against Wawrinka.
"I was just hoping one day my dream was going to come true to play on the regular tour, play Wimbledon, maybe become world number one at some stage.
"So here I am at 300 weeks. It's pretty incredible. Probably one of my biggest accomplishments. I'm very proud of that record, no doubt about it."
Federer first became world number one in February 2004. For a record 237 consecutive weeks, until August 2008, he was top dog, dominating the sport with seemingly effortless grace.
Holder of a record 17 Grand Slam titles, the Swiss said he could still vividly recall the excitement of reaching the pinnacle for the first time.
"It's not one of those moments that happens and then you forget. It took me a lot of great performances to get there," he said.
"It was for me back then sort of the ultimate accomplishment next to winning Wimbledon. That all happened in a span of sort of nine months, which was so intense, huge relief in some ways, but a big satisfaction.
"Yeah, here I am eight years later, even more. It's pretty special. Obviously I lost the world number one ranking a few times but I also stayed a long time once I got there.
"I always felt tennis was easier for me playing as world number one than actually getting there."
Federer said reaching 300 weeks as number one -- which he will achieve when the next rankings are released on Monday -- was reward for all the hard work he had put in over the years.
"I never give up. Show up, tired, injured, doesn't matter how I felt mentally so many times over the years. It's gotten to this incredible number of 300. It's a great reward for me.
"I feel a great sense of satisfaction because of that incredible number and because of all the effort I've put into it. I know how much work it has been. It's not easy to stay at the top for so long."