After leaving school, Middlemiss joined the National Youth Theatre and studied drama at the London Academy of Music and Dramatic Art.
Middlemiss made his debut in Coronation Street in February 1990 as newly-wed Des Barnes together with Amelia Bullmore who played his screen wife Steph.
After leaving Coronation Street, he made only a small number of acting appearances on television, most notably in the role of David Buckley in the ITV drama Where the Heart Is, from 2000 to 2006.
He appeared on a celebrity edition of Come Dine with Me in 2010 with other former Coronation Street stars, Julie Goodyear, Tupele Dorgu and Ken Morley.
[4] He spoke to the press revealing how the false allegations ruined his life as they racked up huge legal costs and left him living in a rented house after his family home was repossessed, as well as it affecting his mental health.