The quartet of Jess Learmonth, Brownlee, Georgia Taylor-Brown and Alex Yee held off the United States and France.
Having claimed bronze in London nine years ago and silver in Rio behind his brother Alistair, Brownlee finished fifth in the individual race on Monday but he played a key role in Britain’s third triathlon medal of the week.
After an excellent first leg from Jess Learmonth, Brownlee broke away from his rivals, and individual silver medallists Georgia Taylor-Brown and Alex Yee maintained the advantage to claim Britain’s seventh gold of the Games.
This is one of a number of mixed events introduced to the programme in Tokyo, although it was added to the Commonwealth Games back in 2014, when Britain triumphed.
Their dominance was stopped soon after, though, and France have won the last three world titles.
The French were well down, though, as Britain, Germany, Holland and the USA formed a lead group, with Learmonth using her fast swim to get out of the water first.
She is not known as the fastest runner but gave everything to stay with American Katie Zaferes, the bronze medallist in the individual race, and collapsed at the finish line.
The same group remained as Brownlee, who will concentrate on long-distance events in the forthcoming seasons, took over, and a swift transition helped him take the lead on the run.
The advantage was nine seconds over the US as he handed over to Taylor-Brown, who extended that to 23 with a brilliant swim.
By the end of her 300 metres swim, 6.7 kilometres bike and 2km run, Taylor-Brown was 22 seconds ahead of the US, putting Yee in a very strong position.
The 23-year-old had serious competition in the shape of American Morgan Pearson and two-time world champion Vincent Luis from France, who soon had Yee in his sights.
He caught the young Kent athlete by the end of the first lap of the bike but Yee sat on his wheel and another impeccable transition saw him surge on to the run in first place.
He never looked like being caught, opening up an 11-second lead on the first lap as Luis’ efforts caught up with him and Pearson moved into silver.
Yee strode down the finishing straight alone before being greeted by his jubilant team-mates, with USA taking silver and France bronze.