The Gloucestershire born actor is to voice Sir Robert Norramby in the 2013 special. The casting comes more than a month after Bob Golding was announced to play Stephen.
Grady is most recognised as Barry Wilkinson in Last of the Summer Wine, the UK's longest running sitcom. He played the role for a number of years from 1986 until the show's demise in 2010.
Other credits include Skins, As Time Goes By, Coronation Street and on film in The Pirates of Penzance and The Return of the Pink Panther.
Grady has also participated in a number of stage shows including Much Ado About Nothing, Hamlet and Peter Pan with the Royal Shakespeare Company.
King of the Railway: The Movie premieres in Vue cinemas nationwide across the UK in late August with September releases due for the US, Germany and Australia.
Thanks to TTTE Wikia for the alert.