A Whig, he became Member of Parliament (MP) for Newcastle-under-Lyme in 1823, being returned for Hastings three years later, and holding for a short time a subordinate position in George Canning's ministry.
Defeated in 1830 both at Newcastle-under-Lyme and then at Liverpool, Denison secured a seat as one of the members for Nottinghamshire in 1831.
After the Great Reform Act he represented the southern division of Nottinghamshire from 1832 until the general election of 1837.
He was appointed High Sheriff of Nottinghamshire for 1839–40.

Denison then represented Malton from 1841 to 1857, and North Nottinghamshire from 1857 to 1872.
In April 1857 Denison was chosen Speaker of the House of Commons.
He was sworn of the Privy Council at the same time.
Re-elected at the beginning of three successive parliaments he retained this position until February 1872, when he resigned and was raised to the peerage as Viscount Ossington, of Ossington in the County of Nottingham.
He refused, however, to accept the pension usually given to retiring Speakers.
Denison gave an explanation – referred to as Speaker Denison's rule – as to how the Speaker should exercise his or her casting vote in the event of a tie.
A Whig, he became Member of Parliament (MP) for Newcastle-under-Lyme in 1823, being returned for Hastings three years later, and holding for a short time a subordinate position in George Canning's ministry. Defeated in 1830 both at Newcastle-under-Lyme and then at Liverpool, Denison secured a seat as one of the members for Nottinghamshire in 1831. After the Great Reform Act he represented the southern division of Nottinghamshire from 1832 until the general election of 1837. He was appointed High Sheriff of Nottinghamshire for 1839–40.
Denison then represented Malton from 1841 to 1857, and North Nottinghamshire from 1857 to 1872. In April 1857 Denison was chosen Speaker of the House of Commons. He was sworn of the Privy Council at the same time. Re-elected at the beginning of three successive parliaments he retained this position until February 1872, when he resigned and was raised to the peerage as Viscount Ossington, of Ossington in the County of Nottingham. He refused, however, to accept the pension usually given to retiring Speakers. Denison gave an explanation – referred to as Speaker Denison's rule – as to how the Speaker should exercise his or her casting vote in the event of a tie.
Evelyn Denison, 1st Viscount Ossington