[3] From 1981 until 1982, he served as a law clerk to Judge James Marshall Sprouse of the United States Court of Appeals for the Fourth Circuit, in Charleston, West Virginia.

[3][4] From 1982 until 1988, Hornak served as an associate at the Pittsburgh law firm Buchanan, Ingersoll & Rooney.

From 1988 until his federal judicial confirmation, he was a partner with the firm, specializing in civil litigation, labor and employment law, media defense, and governmental representation.

[3] For 15 years, he also was solicitor of the Sports & Exhibition Authority of Pittsburgh and Allegheny County.

[4] On December 1, 2010, President Obama nominated Hornak to fill a judicial vacancy on the United States District Court for the Western District of Pennsylvania that had been created by the transition to senior status in November 2010 by Judge Donetta Ambrose.