British triathlete, who won in London and Rio, intends to try for hat-trick at Tokyo 2020.
Speaking to BBC Sport, the 31-year-old says the lure of a fourth Games proved hard to ignore.
"The decision crept up on me a bit: I want to go to another Olympics, and I want to see what I might be able to do," he said.
"I'm happy, because I want to be racing on the biggest stage, and being competitive. The 12-year-old me dreamed of going to one Olympics. So to pass up the chance of just seeing where it leads me this year would be a bit mad."
Brownlee, who beat younger brother Jonny at both London 2012 (where Jonny won bronze) and Rio 2016 (silver), has recently taken time off from the International Triathlon Union's World Triathlon Series, the main qualification method for the Tokyo Games.
Great Britain currently sit fifth in the ITU's mixed relay Olympic qualification rankings, and need to be in the top seven teams on 31 March to qualify two male and two female athletes for the Games.
The British Triathlon Federation would have the right to nominate any athlete for the quota spots, but the older Brownlee's absence from major ITU competition currently ranks him sixth among British men in the Olympic rankings and 139th overall in the ITU World Rankings. He hasn't won a World Triathlon Series race since June 2017.
"I need to look at it one step at a time," he said in his interview. "Do some World Series racing, see how competitive I am. Try to qualify, see how that goes."
His last World Series race, on home soil in Leeds in 2019, ended with a disappointing 44th-place finish.
After retaining his Olympic title at Rio 2016, the Yorkshire-based athlete announced he would spend a couple of years focusing on the longer triathlon distances, including IronMan events.
Brownlee competed in the 2019 World IronMan Championships, finishing 21st behind the last man to win Olympic triathlon gold before him, Jan Frodeno.
He then won a race in Western Australia, qualifying for the 2020 championships and throwing up a dilemma: continue the endurance training regime, or race at Tokyo?
While not ruling out doing the endurance race in Hawaii in October, he told the BBC there was only one choice for him if he could only win one.
"I'd rather win the Olympics again. It means a hell of a lot; there is something very special about the Olympics.
"Whoever you are around the world, the Olympics is always special."