John was born in December 1946 in New York, to Mildred, a waitress, and John Speshock, a truck driver. He is of Irish and Ukranian descent.
At 16 he attended the Professional Children's School in New York, and later Fairleigh Dickinson University, but did not finish his degree.
His TV work began in The Patty Duke Show, but is best known to audiences for his roles on LA Law and The West Wing.
John passed away in December 2005, just a few days before his 59th birthday, and his death was tastefully included in The West Wing.
He lived with his long-time girl friend, actress-choreographer Patricia Mariano up until his death.