They will be joined by Joe Meyer, Caroline Powell and Heelan Tompkins in Hong Kong where the Olympic equestrian events will be held.
After eight years in retirement, Todd has completed a successful return to the elite level with inclusion this year and in Beijing he will join Nicholson as New Zealand's most capped Olympian.
The pair will be attending their sixth Olympic Games, surpassing canoeist Ian Ferguson's attendance at five Games.
New Zealand Olympic Committee secretary general and selector, Barry Maister, today said the eventing announcement was particularly special.
"Mark Todd and Andrew Nicholson are among our finest Olympians and to have athletes attending their sixth Games is testament to the depth of talent we have in New Zealand sport," he said, hours after the eventing team was leaked, with details appearing in Britain's Horse & Hound magazine before the official announcement.
"I think it is a fantastic team and we have high hopes for them."
Widely regarded as one of the greatest riders of all time, Todd, a gold medallist at Los Angeles in 1984 and Seoul 1988, was delighted to get the seal of approval after a late bid for inclusion.
"I'm delighted that we've got the nod to go," he said.
"It's what we set out to do at the beginning and we're looking forward to being part of the team.
"New Zealand has a good, solid team - they're all pretty strong, fit and sound - so we've got a good chance of going really well out there."
Britain-based Nicholson, known for his consistency on the European eventing circuit, is continuing an Olympic association that started at Los Angeles in 1994.
He has been a regular top-10 performer over a number of years and holds the record for the most number of Badminton completions, which is regarded as the world's most prestigious four-star event.
"It's a pretty good team," Nicholson said. "It's better than what it could have been a couple of years ago and it's getting stronger all the time.
"We have a good chance of winning a team medal."
Meyer, who has been based in Britain for several years, will be making his Olympic debut in Hong Kong.
"It's what I've been aiming for for years; I've always wanted to go to the Olympics," Meyer said.
"Competing at Badminton, Burghley, the world champs and the Olympics - that's what it's all been about.
"I'm very excited and I want it to go very well. It's good to be selected but now I want to win a prize."
Powell, formerly from Canterbury and now based in Scotland, will also make her debut in Hong Kong.
A big improver in recent years, Powell reached a career highlight and the best European performance by a New Zealander this season when finishing fourth at Badminton.
"It's great and I was kind of hopeful," she said.
"I think we've got a good depth of team and that we have as much chance as anyone. As long as things come together we're in with a good chance."
Taranaki's Tompkins completed her selection buildup in Britain.
She made her Olympic debut in Athens four years ago where she was the best of the New Zealand team in seventh place, the same placing she achieved at the World Equestrian Games in 2006.
"This is the most excited I have been of any of the teams I have been in so far," Tompkins said.
"The riders are individually strong and hopefully together it will produce a medal result."
New Zealand team and mounts: Mark Todd (Gandalf), Andrew Nicholson (Lord Killinghurst), Caroline Powell (Lenamore), Joe Meyer (Snip), Heelan Tompkins (Sugoi).
