Sibthorp was born into a Lincoln gentry family, the son of Colonel Humphrey Waldo Sibthorp, of Canwick Hall, by his wife Susannah, daughter of Richard Ellison, of Sudbrooke Holme, Lincolnshire.

[1][2] He was commissioned into the Scots Greys in 1803, promoted lieutenant in 1806, and later transferred to the 4th Dragoon Guards, in which he reached the rank of captain.

[2] During Sibthorp's three decades in Parliament, he became renowned, along with Sir Robert Inglis, as one of its most reactionary members.

His political views, his bluntness in expressing them, and his eccentricities made him the target of both witticisms and cartoons in Punch.

Sibthorp died at his home in London, and was succeeded as MP by his son, Gervaise Waldo-Sibthorp.