Pierrepont was styled Viscount Newark after the death of his elder brother in 1850. In 1851, he was commissioned a captain in the South Nottinghamshire Yeomanry Cavalry, and in 1852, was elected unopposed as Conservative Member of Parliament for South Nottinghamshire. He was named a deputy lieutenant of Nottinghamshire in 1854.
Pierrepont assumed the title Viscount Newark upon his brother's death in 1850. In 1851, he received a military commission as captain in the South Nottinghamshire Yeomanry Cavalry, and two years later, he was elected unopposed to Parliament as Conservative MP for South Nottinghamshire. He was appointed deputy lieutenant of Nottinghamshire in 1854.