Baron Rendlesham, of Rendlesham, is a title in the Peerage of Ireland.^[1] It was created in 1806 for the businessman Peter Thellusson, who also represented Midhurst, Malmesbury and Bossiney in Parliament. The Thellusson (pronounced "Tellusson") family were of French Protestant origin, but settled in Geneva, Switzerland, after the St. Bartholomew's Day massacre of 1572.

A later member of the family, Peter Thellusson, emigrated to England in 1762 where he established a successful London business. From the wealth acquired, he purchased several estates around the country, notably Brodsworth Hall in South Yorkshire. After his death his estate was embroiled in the Thellusson Will Case.

His eldest son was the aforementioned Peter Isaac Thellusson, 1st Baron Rendlesham, who took over the family business. Lord Rendlesham's younger son, the fourth Baron (who succeeded his twin brother), sat as a Member of Parliament for Suffolk East. His only son, the fifth Baron, also represented this constituency (as a Conservative). As of 2013^[update] the title is held by the latter's great-grandson, the ninth Baron, who succeeded his father in 1999.