From 1996 to 2018, Horan served as a judge of the Butler County Court of Common Pleas in the civil division.

During her tenure on the state bench, she also presided over civil and family law cases.

[2] On July 30, 2015, President Obama nominated Horan to serve as a United States District Judge of the United States District Court for the Western District of Pennsylvania, to the seat vacated by Judge Terrence F. McVerry, who assumed senior status on September 30, 2013.

On December 20, 2017, her renomination by President Donald Trump was announced and sent to the United States Senate.

[6] Horan was nominated to the seat vacated by Gary L. Lancaster, who died on April 24, 2013.