The pair, team-mates in 2021-23 at the Arrow McLaren IndyCar Series squad, will make one-off appearances at Daytona on 27-28 January in the pair of LMP2 class ORECA-Gibson 07s run by the Anglo-America team co-owned by McLaren Racing boss Zak Brown.
O’Ward, who is remaining at Arrow McLaren for a fifth season in 2024, will share United’s #2 ORECA with full-season drivers Ben Keating and Ben Hanley, as well as Nico Pino, who will contest the long-distance rounds in the car.
Rosenqvist, who is switching to Meyer Shank Racing for his 2024 IndyCar campaign, will race the sister #22 car with Paul di Resta and Dan Goldburg, while the fourth driver who will also contest the remaining four IMSA enduros has yet to be announced.
Ward will be bidding for a third class victory at the Daytona enduro.
The Mexican won on debut in 2017 in the Prototype Challenge division aboard the one-make ORECA-Chevrolet FLM09 as part of a full-season programme with Performance Tech Motorsports that yielded the class title.
He won in P2 aboard a DragonSpeed ORECA in 2022, his most recent appearance at the Daytona International Speedway.
United team principal Richard Dean said: “We have been trying to get Pato in a United car for a while now; after a few false starts, finally we have our man.
“Pato brings experience as a Daytona race winner and is just plain fast in everything he drives.”
Rosenqvist is making a return to endurance racing for the first time since 2018 when his programme included a second Daytona campaign after a 2016 debut.
The Swede’s sportscar experience includes racing in the GT World Challenge Europe, Super GT in Japan and the Le Mans 24 Hours.
Dean described Rosenqvist as a “winner who has won races across an impressive range of series through his career”.
United will be racing at Daytona in January as part of its first full-season attack on the IMSA series.
Its LMP2 team is effectively moving to the North American series after the disappearance of the class from the World Endurance Championship at the end of this season.
The best result for United at Daytona came in 2018 when it finished fourth overall with a line-up including di Resta and Bruno Senna driving a Ligier-Gibson JSP217 when P2s raced as part of the top class alongside the Daytona Prototype internationals.
