Armstrong’s departure from the Ganassi squad was expected with the team downscaling from five cars to three.
The New Zealander will still have some connection to Chip Ganassi Racing through a technical alliance between the two teams.
The 24-year-old will pilot the #66 entry alongside Sweden’s Felix Rosenqvist, who will continue in the #60 entry.
After a part-time campaign in 2023 where he finished 20th in the points, Armstrong improved to 14th in 2024 in a season that included one podium at Detroit and five top five finishes.
“I’m very proud to be joining Meyer Shank Racing in 2025,” said Armstrong.
“I had a great feeling when I met both (co-owners) Mike Shank and Jim Meyer, their passion for performance and meticulous work ethic was obvious from our first conversation and I want to thank them both for this opportunity.
“I’m looking forward to getting to know everyone at MSR over the off-season with the goal of hitting the ground running at the first race of the season in St Pete.
“This year I got closer to where I want to be performance-wise, including oval racing for the first time and I’m looking forward to continuing to push up the order with MSR. We want to be at the front, fighting for wins and I believe we have the recipe to do it.”
Armstrong replaces AJ Foyt Racing-bound driver David Malukas who has joined that team on a multi-year deal.
Meyer Shank Racing co-owner Mike Shank hailed Armstrong’s arrival.
“We’re very excited to welcome Marcus on board,” said Shank.
“He’s really shown a lot of growth and consistency in his first two years in IndyCar, which is really difficult to do.
“This series is probably one of the most competitive series out there and he has proven himself to be a real contender.
“We are going to do everything we can to give him the car and the tools to produce results next year.”