The London and Rio champion had refused to commit either way over the last three-and-a-half years but has now made his mind up in favour of another tilt at gold.
Brownlee told the BBC: “A year ago I wouldn’t be doing this because I knew I couldn’t cope with another bad injury. I just wanted to be able to run and compete and enjoy it.
“But in the past year I haven’t been injured. I’ve really enjoyed training and I’ve really enjoyed competing, and preparing to compete. And so 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.”
Brownlee has raced sparingly over the Olympic distance since Rio, and with substantially less success than he had been accustomed to.
His last victory in the elite world series came in his home city of Leeds back in 2017, although he did win a fourth European title last June.
Brownlee’s first task will simply be to qualify for the British team and, should he make it, he insisted his marker of success extends beyond gold.
The 31-year-old 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.
“In my head, the perfect scenario is that I’m in a position where I’m stood on the start-line and I think I can win the race. But, if I’m instead thinking I can scrape a third here, or I’m thinking I could help another British athlete win a medal here, I would be happy with that. I would.”