O'Mara was most well known in the U.S. for her role of Cassandra "Caress" Morrel on the soap "Dynasty," which aired on ABC from 1981 to 1989 -- the primetime counter to CBS's "Dallas." O'Mara's character Caress was the sister of Alexis Colby, played by Joan Collins -- the show's primary star.
Upon learning the sad news today, Collins tweeted her condolences.
Tragic news about Kate O Mara , we had great fun on Dynasty when she played my sister Caress who Alexis insisted on calling CASSIE ! RIP— Joan Collins (@joancollinsobe) March 30, 2014
In the U.K., O'Mara was recognized for her work on several British TV dramas, including "Howards' Way" and "Triangle," as well as "Doctor Who."
In her later years, O'Mara wrote two novels, When She Was Bad and Good Time Girl, as well as two memoirs.
Her agent said that the actress died at a nursing home in Sussex, England, after briefly battling an undisclosed illness.
"She was extraordinary, she had so much energy and vitality with a love for theatre and acting," Belfield told The Mirror.
He added: "A shining star has gone out and Kate will be dearly missed by all who knew and have worked with her."
She leaves behind her sister, actress Belinda Carroll.