They are linked by Samuel Hinkley of Cape Cod, who died in 1662.
Mr Obama is also a distant cousin of the actor Brad Pitt while Hillary Clinton is related to Mr Pitt’s girlfriend, Angelina Jolie.
The ties of the US Democratic rivals were established by a respected US genealogical organisation after three years’ investigation.
Mrs Clinton and Mr Obama can also boast a long list of other famous relations.
Christopher Child, from the New England Historic Genealogical Society, says that the politicians’ ancestries show they have more in common than they think.
The Society, founded in 1845, is the oldest and biggest non-profit genealogical organisation in the United States.
The research, conducted by Mr Child and Gary Boyd Roberts, came up with some extraordinary family connections.
Mr Obama is the son of a white woman from Kansas and a black man from Kenya.
He was previously identified as a distant cousin of US Vice-President Dick Cheney.
His political lineage includes not just President Bush but also Gerald Ford, Lyndon Johnson, Harry S Truman, Dick Cheney and Winston Churchill.
The connection made with Hollywood star Brad Pitt adds a welcome splash of glamour to his family tree.
But Mrs Clinton’s kin has much more of an exotic feel.
Her distant cousins include the singers Madonna, Celine Dion and Alanis Morissette, as well as the beatnik author Jack Kerouac and Prince Charles’s wife, Camilla Parker-Bowles.
She and Angelina Jolie are ninth cousins, twice removed. They are both related to one Jean Cusson, who died in St Sulpice, Quebec, in 1718.
