The more than 100 artifacts had been in the possession of King's close friend and personal secretary, Maude Ballou, 88, for more than half a century.
Eight cards of handwritten notes for a speech that King gave to bid farewell to his congregation at the Dexter Avenue Baptist Church in December 1959 fetched $31,250.
Other highlights were two letters King wrote to Ballou from India where he studied Gandhi's philosophy of non-violence that went for $18,750 and $17,500.
Two autograph draft chapters from his first book "Stride Toward Freedom" were also sold for $8,125 each.
The US civil rights leader and Nobel Peace Prize laureate, who campaigned for racial equality and an end to discrimination, was assassinated on April 4, 1968.
Sandra Palomino, director of historical manuscripts at Heritage, said the material provided "a ground-level perspective of the civil rights struggle."
"There was worldwide interest in the material and the emotional response to it was huge," she said.
The items were sold as part of a two-day auction of historic manuscripts in New York that continues Friday.