Denzil Roberts Onslow (15 June 1839 – 21 March 1908) was an English Conservative Party politician who sat in the House of Commons from 1874 to 1885. He played first-class cricket for Cambridge University from 1859 to 1861, Sussex from 1860 to 1869 and for Marylebone Cricket Club (MCC) from 1861 to 1873. Onslow was a right hand batsman and played 40 innings in 23 first-class matches with an average of 10.70 and a top score of 53. He was a right-arm fast bowler and took 20 wickets at an average of 18.35 and a best performance of six wickets in an innings.