Þórðarson is a surname of Icelandic origin, meaning son of Þórður. In Icelandic names, the name is not strictly a surname, but a patronymic. The name is sometimes written Thordarson and may refer to:

• Björn Þórðarson (1879–1963), Icelandic politician; Prime Minister of Iceland 1942–44
• Chester Thordarson (born Hjörtur Þórðarson) (1867–1945), inventor who held nearly a hundred patents
• Fridrik Thordarson (1928-2005), Icelandic linguist
• Guðjón Þórðarson (born 1955), Icelandic professional football manager
• Guðlaugur Þór Þórðarson (born 1967), Icelandic politician; member of the Althing since 2003
• Óláfr Þórðarson (1210–1259), Icelandic scholar and skald
• Ólafur Þórðarson (footballer) (born 1965), Icelandic professional football player
• Sigurdur Thordarson (born 1992), FBI informant against Julian Assange
• Sigurjón Þórðarson (born 1964), Icelandic politician
• Sigvatr Þórðarson (fl. 11th century), court poet to kings of Norway
• Stefán Þórðarson (born 1975), Icelandic professional football player
• Stefán Teitur Þórðarson (born 1998), Icelandic professional football player
• Sturla Þórðarson (1214–1284), Icelandic chieftain and writer of sagas
• Teitur Thordarson (born 1952), Icelandic football coach
• Þórbergur Þórðarson (1889–1974), Icelandic author and Esperantist