Alonso took part in some 95 Grands Prix races for McLaren over two spells, and also drove for the team at the 2017 Indianapolis 500.
McLaren confirmed the Spaniard, 37, was set to “stay closely connected” to its activities “helping advise the team’s drivers and engineers.”
Alonso is also set to drive at selected tests to support the development of MCL34 and MCL35 ahead of the 2020 campaign.
Later this year, Alonso will race for McLaren as he looks to land the Indianapolis 500 title, aiming to become only the second driver to complete motorsport’s Triple Crown, having already landed victory in the Monaco Grand Prix and the Le Mans 24 Hour.
Alonso said: “Becoming a McLaren ambassador is a true honour. It 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.”
Norris, meanwhile, was fastest on the opening day of F1’s second pre-season test in Barcelona.
The 19-year-old set the pace ahead of Red Bull’s Pierre Gasly, although he also twice had to be recovered from the track as the rookie’s development continues.
Alonso claimed the F1 drivers’ championship title in 2005 and 2006 with Renault, becoming the youngest ever double world champion at the time.
The Spaniard added: “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.”
McLaren chief executive Zak Brown said: “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.”
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies