In 1673, Blackett was elected in a by-election as Member of Parliament for Newcastle-upon-Tyne in the Cavalier Parliament. He was created a baronet nine days later on 12 December 1673 and the fee was remitted "in consideration of his good services". He was commissioner for assessment for county Durham and Northumberland from 1677 until his death and commissioner for carriage of coals for the port of Newcastle in 1679. He retained his seat at Newcastle in the two elections of 1679.