Born Charles Sackville, he was the eldest son of Lord George Sackville. Charles' father changed the family surname to Germain in 1770 and Charles re-incorporated the former surname as a double-barrelled one later in life.
From 1776 to 1815, Germain was Receiver General of Jamaica. In 1785, he inherited his father's viscountcy of Sackville and then his cousin's dukedom of Dorset in 1815. He was appointed a Privy Councillor and Master of the Horse in 1821. Serving in that office until 1827 and again in 1835, he was also appointed a Knight of the Garter in 1826.
Dorset died unmarried and childless in 1843 and all of his titles became extinct.