 He succeeded to the Baronetcy of Belsay Castle on the death of his grandfather in 1867.His grandfather had changed his name from Middleton to Monck in 1799, and in 1876 the 7th Baronet and his brothers changed their name from Monck back to Middleton.He was elected as a Liberal Party Member of Parliament (MP) for the City of Durham at a by-election in 1874, after the 1874 general election in Durham had been voided on petition.