The stylish Bell rescued his side from a sticky situation at 49 for three, hitting 105 not out to lead England to 234 for five at the close of play on day three of the fourth test in County Durham - an overall lead of 202 runs.
David Gower (1985) and Maurice Leyland (1934) are the only other Englishmen to chalk up three tons in a home Ashes series.
Asked by reporters if it was proving to be a career-defining summer, the 31-year-old Bell replied: "I haven't thought of it like that. It's just nice to contribute.
"There will be time to think about that when I've finished with cricket."
Paceman Ryan Harris put Australia on top with an early new-ball burst that removed Joe Root, Alastair Cook and Jonathan Trott.
Kevin Pietersen (44) then joined Bell in the middle and the duo hauled England, already 2-0 up in the five-match series, back into the game with a stand of 106 for the fourth wicket.
"It's good to have Kev back in form," said Bell after notching the 20th test century of his career. "I think this is teed up for a great match - the next two days are going to be very exciting.
"With Kev we have got completely different strengths. The similar balls that are bowled we hit in different places so it works really well. He's good fun to bat with."
Bell struggled to make an impression on Australian bowling greats like Glenn McGrath and Shane Warne at the start of his career but he has blossomed into a world-class batsman.
"I believed I was good enough to score test hundreds against Australia but it did take a while," he said. "My first two series were against arguably one of the best teams of all time.
"As a young player that was a real baptism. I learnt a lot from some great players.
"It's been enjoyable this time to score some hundreds and maybe put to bed some of the stuff I have done in the past," added Bell who also hit 109 in the first test in Nottingham and 109 in the second test at Lord's.
(Editing by Martyn Herman)
