The American, who won the doubles title at Flushing Meadows with Yaroslava Shvedova back in 2010, is one of eight wild-card recipients.
King, a former top-50 player, will be playing in her ninth US Open. She has slid down the rankings in recent times and is currently at number 140.
Her compatriots Alison Riske and Maria Sanchez also found out on Wednesday they would be playing in the main draw in New York.
Shelby Rogers had already earned her wild card thanks to her recent efforts on the US Pro Circuit, while national 18-and-under champion Sachia Vickery had also guaranteed her spot. Nicole Gibbs also claimed a wild card by winning the national collegiate title for the second year in a row.
The other two wild cards go to Australian and French players under an agreement the USTA has with those countries' tennis federations.
Teenager Ashleigh Barty gets the Australian one with Pauline Parmentier being France's representative.