William King Sebastian (June 12, 1812 – May 20, 1865) was an American politician, judge, and lawyer from Helena, Arkansas.

[2] When the American Civil War began, "he did not resign, as did all the other southern senators save Andrew Johnson, but remained a melancholy and helpless spectator of events".

[1] Sebastian left the Senate and went back to Helena, where he resided and worked as a lawyer during the Civil War.

After federal troops occupied Helena, he moved to Memphis, Tennessee, in 1864 and resumed the practice of law; he died there on May 20, 1865, and is buried in a private family cemetery in Phillips County.

In 1877, the Senate revoked the resolution of expulsion which they had passed upon Sebastian, and consequently paid the compensation due to his children.