Yes, John Mills did act in several TV series, including "The Moonstone" in 1958, "The Forsyte Saga" in 1967, and "A Man Called Horse" in 1968. He also appeared in a number of TV movies, such as "The Life of Emile Zola" in 1968 and "The Three Musketeers" in 1973.
The Extraordinary Journey of John Mills: A Captivating English Quiz