In English, name Brett means – A native of Brittany: (France) or Britain: (England). Derived from the surname Breton or Briton, Brett and Bret became popular first names after 19th-century US writer Bret Harte. Brett became very popular in Australia in the mid-20th century.. Other origins for name Brett include – English, Irish, Celtic, French. Name Brett is a unisex name and can be used for a boy or girl name (male or female).