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's rise to prominence began after his brother's death in 1850, when he took on the title Viscount Newark. The following year, he received a military commission as captain in the South Nottinghamshire Yeomanry Cavalry, and two years later, he won an uncontested election as Conservative MP for South Nottinghamshire. He was subsequently named deputy lieutenant of Nottinghamshire in 1854.