Kay filed Tuesday in Frankfort, a day after party leaders nominated him to run in a June 25 special election to replace former state Rep. Carl Rollins of Midway. Rollins resigned to become head of the Kentucky Higher Education Assistance Authority.
Also Tuesday, district Republicans nominated Lyen Crews of Woodford County to run for the seat.
The 30-year-old Kay, an attorney from Versailles, is making his first bid for public office. He previously worked on the legislative staff of House Speaker Greg Stumbo.
Crews ran unsuccessfully against Rollins in 2010 for the seat that represents Woodford County and portions of Fayette and Franklin counties.