Gold medallists Brownlee, Alex Yee, Georgia Taylor-Brown and Jess Learmonth will all be in action.
The relay made its Games debut this summer as one of a number of new mixed events and was a big hit – something that came as a welcome surprise to Brownlee.
He told the PA news agency: “We didn’t quite realise the impact the mixed team relay had and the amount of people that watched it. We were kind of in our own little bubble in Tokyo.
“It wasn’t until I got home I realised how popular it was. It was absolutely amazing.
“You’ve got different audiences – you’ve got the triathlon audience, who are always going to watch it, then you’ve got the general sports people and the people who aren’t even sports fans, and I think the mixed team relay captured all of them.
“People turned it on and were like, ‘Wow I really like this’. I’ve had loads of people come up to me in the street, in the supermarket, and say they’ve never watched triathlon before and they absolutely loved it.”
Sunday’s race will be the first time Super League has hosted a Championship Series event in the UK, and Brownlee expects the format to be popular both live and on TV, with the athletes competing in three quickfire races that mix up the traditional swim-bike-run order.
“It’s a really, really cool venue here,” said the Yorkshireman. “It’s the kind of venue Super League should be at. I know what a home London crowd is like and I think a lot of people will come down here.
“It will even be weird for us racing in front of a crowd, we haven’t done that for a while. I think it will be a great event. It will obviously be short, fast, it will be hard, and it will look really cool.”
The relay gave Brownlee a much-coveted first Olympic gold medal at his third Games and looked like the perfect way to close that chapter of his career.
But the 31-year-old was so impressed with his performance – he posted the fastest leg of the race having finished fifth in the individual event – that he put a fourth Olympic appearance in Paris in 2024 straight on the table.
“It’s probably one of the best performances I’ve ever had so that made me believe maybe I could do it again, if not be even better,” said Brownlee.
“I also didn’t realise how much the Olympics captures you and takes hold of you. It is an unbelievable event.
“I’m going to do a bit of different racing next year. I want to do some more Super League racing, some World Cups, some World Series racing, a couple of long distance races, just do some racing I really enjoy without the constraints of the Olympic calendar.
“The end of next year I’ll definitely make a commitment because, if I want to perform, I think you have to commit two years before.”
Jonny’s older brother Alistair left Olympic racing behind after failing to qualify for Tokyo and will focus on longer-distance events.
This weekend sees him take on Badlands, an unsupported off-road bike race in Spain of 750 kilometres.
“I think he’s absolutely crazy,” said Jonny with a chuckle. “I can’t work out if it’s going to be one of those experiences when you finish and go, ‘That wasn’t too bad’, or you go, ‘That was the worst thing in my life’.
“Alistair’s strength is also his weakness in that he’s tough, and he’ll probably battle through bits where he’s better off going to bed for a couple of hours.”
The brothers are very different characters, and Jonny cannot see himself attempting a similar challenge.
“I think that’s too long for me," hy het gesê. “I like the idea that I can do anything as long as it involves a warm meal at the end of the night, a nice shower and a bed.”