Ferrer, who is set to step down from his role as Spain's Davis Cup captain after this month's Finals, will join Ruud's father Christian and Pedro Clar in the 27-year-old's team.
The Spaniard, a French Open finalist in 2013, coached Alexander Zverev in 2020 and 2021 shortly after his retirement as a player in 2019.
"Good news travels fast! David Ferrer will be joining the team next year, and needless to say, we're all really excited about what's ahead," Ruud wrote in a post on Instagram after his 6-4, 6-4 loss to Alcaraz on Saturday.
The appointment comes after a disappointing campaign for Ruud, a three-time Grand Slam finalist and former world number two.
He has not won a title in 2026, the first time that has happened since 2019, dropping to 23rd in the world rankings.