The 29-year-old two-time Wimbledon champion has been chosen to lead out Team GB at the 80,000-seated Maracana Stadium.
The ceremony, choreographed by creative director Fernando Meirelles, is expected to include a spectacular display of fireworks, a focus on carnivals, dancing and theatre despite budget cuts curtailing some of the razzmatazz of such a world event.
A total of 206 countries are taking part with 10,500 athletes taking part in a range of 42 sports, with golf and rugby back on the list.
Speaking on the BBC’s Good Morning Scotland radio programme, Judy Murray said: “Everyone can see from the way that he approaches the Davis Cup. He loves representing the country, he loves team competition, and I know that when he was at the Olympics in London – particularly that whole sense of being part of a much bigger thing than just the tennis – it was a massive, massive thing for him.
“I just get the feeling that at this Games – he’s been through Beijing and London, he knows what it’s all about so he has a much bigger sense of the duty and the occasion and of course the opportunity, so I think he’s going to find it a little bit emotional.”
Murray said he was “speechless” and “honoured” was chosen by a British Olympic Association panel.
“The privilege of being the flag bearer is a moment I will remember for the rest of my life and will certainly be one of the highlights of my career.
“It’s a huge honour to represent Team GB at an Olympic Games for the third time.”
Murray, whose second Wimbledon title came last month, follows fellow Scot and cycling champion Sir Chris Hoy, who led out Team GB at London 2012.
First Minister Nicola Sturgeon has sent a message of support to Team GB and the 53 Scottish Olympians taking part.
Swimmer Michael Phelps, the most decorated Olympian of all time with 22 medals, is the US standard bearer.
Describing his hopes for the opening ceremony, Meirelles who directed City of God, the four-time Oscar nominated movie, said the ceremony would be vision of the country “and what I hope it will become”.