Rawlins Lowndes entered South Carolina's colonial administration as provost marshal in 1745, learning legal practice through office. Elected to the Commons House in 1749, he represented plantation interests and served on important committees. He became speaker in 1763 and again in 1772. His defense of the assembly's privileges brought conflict with royal officials, although he continued hoping for reconciliation with Britain.

As an assistant judge from 1766, Lowndes supported opening courts despite the Stamp Act and challenged claims that the Royal Council possessed the standing of Britain's House of Lords. During the Revolution he served in the provincial congress and Council of Safety. After John Rutledge resigned over the proposed state constitution, the legislature elected Lowndes president in March 1778. He served less than a year, facing British pressure and disputes over committing South Carolina's militia and supplies to wider Continental operations.

Lowndes withdrew from executive office in 1779. During the British occupation he sought restoration as a British subject, a choice that temporarily cost him full citizenship in the restored state. He returned to the legislature from 1787 to 1790 and opposed the federal Constitution in 1788, fearing northern commercial power and restrictions affecting slavery and the slave trade. He also served a term as Charleston's intendant. He rebuilt his estate after wartime losses and died in Charleston in 1800.