Pagenaud has been forced onto the sidelines ever since a heavy crash in practice for the Mid-Ohio round in July, triggered by an apparent brake failure, left him with post-concussion symptoms and curtailed his campaign.
A host of drivers have filled in for the 2019 Indianapolis 500 winner, with former Ed Carpenter Racing driver Conor Daly, MSR's IMSA champion Tom Blomqvist and Indy NXT champion Linus Lundqvist each taking turns at the wheel.
Lundqvist has since signed for Chip Ganassi Racing, while Blomqvist will take over the sister MSR car full-time as Helio Castroneves moves into an Indy-only programme with a third entry.
With Pagenaud's future in question, MSR has turned to Rosenqvist who has signed a multi-year agreement.
“I’m super excited to start the next chapter of my IndyCar career together with MSR,” said Rosenqvist. “This will be a great opportunity for myself and MSR to elevate and get to the next level together.
“I’m also pretty excited to get to work with my old friend Tom again. I’m ready to start working together and getting the next season started.”
Source: Autosport