0929 GMT June 15, 2019
The team said Alonso would "help advise the team's drivers and engineers and drive at selected tests to support the development" of the 2019 and 2020 cars, BBC wrote.
The Spaniard, 37, left F1 last year and is competing at the Indianapolis 500 this season for a McLaren team.
Alonso said the role was "a true honor" and "just the beginning".
He added, "McLaren is a special team, and despite the challenges we have endured recently, it remains so.
"I said before I stopped racing in Formula 1 last year that I see myself with McLaren for a long time to come, so I am delighted at this new role and the ability to stay closely involved with the team I feel is my spiritual home.
"We have the Indianapolis 500 in May of course, which I am looking forward to immensely, but this is just the beginning of many things we can do together.
"I am particularly passionate about nurturing young talent, whether that's with my own team or helping the new generation of Formula 1 drivers at McLaren unlock their true potential.
"This is important to both the team and myself, so will be an especially rewarding part of my role."
Alonso, who has set up his own karting circuit and school in his home town of Oviedo in Spain, hopes to win the Indy 500 this year and become only the second driver in history to win motorsport's unofficial 'triple crown' of Monaco Grand Prix, Le Mans 24 Hours and Indy. Some regard the F1 part of the achievement as the world title.
McLaren chief executive Zak Brown said, "Fernando is part of the McLaren family. He has set his place in the team's history and continues to write his chapter of the McLaren story, so it is entirely appropriate that we formalize his status as a McLaren ambassador, joining another double champion, Mika Hakkinen.
"For any race team, having someone of Fernando's class on hand to provide support through his experience is of huge value.
"His insights and perspective will be welcomed by both our drivers and engineers alike, while his stature and character remain highly appealing to our partners and fans."
Could Alonso return to F1?
In a news conference at preseason testing in Spain, Alonso also hinted that he had not shut the door on a potential F1 return at some stage.
"I feel at the peak of my career so probably being at home is a waste of time and possibilities for everyone," he said.
"I am doing different iconic races now. I feel at the best moment of my career and I hope to win as many races as I can and I keep involved in the F1 life in case.
"I am probably stronger than ever now at 37, physically, mentally and knowledge of different driving styles.
"I feel very competitive in any series I jump in, so I will keep going the next couple of years and see what races will make an impact and race those.
"If one day F1 arrives the moment I can be competitive and be winning, I cannot be relaxed at home.
"I need to keep updated and the way to keep me updated in the moment is to be involved somehow."