The central midfielder has penned a two-year contract with the Rams.
English League One club Derby County announced the signing of Republic of Ireland midfielder Conor Hourihane.
The central midfielder has penned a two-year contract with the Rams, running until the summer of 2024, after successfully completing a medical.
Hourihane, who has played almost 500 career matches, has been a sought-after figure in the EFL this summer but Derby have been able to beat off strong competition to secure his services.
31-year-old Hourihane has agreed the deal with the club, having been released by Aston Villa last month.
The midfielder was a regular throughout his two-and-a-half seasons with Villa in the Championship.
He scored 11 times in 46 appearances in 2017/18, including a hat-trick against Norwich City, as Villa lost the Play-Off Final to Fulham, while nine in 48 followed in 2018/19 as the West Midlands outfit defeated Derby in the 2018/19 Play-Off Final to gain promotion.