The actress has landed a potentially recurring role in the USA series, TV Line reports.
Zimmer is expected to play Dr Abby Burton, a psychiatrist and old friend of Hank (Mark Feuerstein).
Hank asks Abby for help with an important patient, and rumours have suggested that she could be a love interest for him.
Zimmer has previously starred in shows including Joan of Arcadia, Boston Legal and Entourage.
She recently played Colleen in NBC's Love Bites and joined the CBS pilot Home Game, which was not picked up.
Her appearance on Royal Pains is expected to be broadcast towards the end of the current third season, which airs on Wednesdays at 9/8c on USA.
Matt Lauer and Julie Benz have also landed roles in this season of Royal Pains.
Watch a trailer for the next episode of Royal Pains below: