Macgregor, 27, will take on the world’s best in the Olympic Test Event held this August in Rio, the host city of the 2016 Olympics.
She and her crew Andrew ‘Walshy’ Walsh are aiming for success in the Nacra 17 class, which replaced the Elliot 6m class in which Macgregor competed at London 2012.
The Poole sailor described the event as “the first big step along the journey” towards fulfilling her medal-winning ambitions.
“We’re really pleased to have been selected for the Test Event in Rio this year – it’s a big deal,” she said.
“It’s a big step along the journey, getting a taster for what Rio’s like, and what the sailing’s going to be like in two years’ time.
Macgregor switched to the two-person Nacra 17 after her Elliot 6m match racing event – the event she competed in at London 2012 with younger sister Kate and fellow Poole sailor Annie Lush – was removed from the Olympic programme.
“The Nacra couldn’t be more different really,” she added.
“It’s a fantastic boat, I’m really enjoying the challenge of getting into something completely different and new. “It does mean there’s a hell of a lot to learn, but that’s no bad thing. It’s great having that new challenge.
“As a new class there’s a hell of a lot to work out in terms of how to sail them as quick as possible. No-one has the answers at the moment.”
Macgregor has put the disappointment of London 2012 – in which her promising team missed out on a medal – behind her and now has her sights firmly set on winning in Rio.
“We had the potential, so that hurt even more, but that does mean that this time round we’re even more hungry for it,” she said.
“I’m super excited about this campaign that I’m in, and this campaign with Walshy is brilliant. “I want to do it right this time and get that medal.”
The regatta is the first official Test Event for any Olympic sport, and will see British sailors competing across the ten Olympic Classes on the 2016 racecourses in Guanabara Bay.
The event runs from August 2 to 9.