The second-term councilman and former Springfield commissioner said he planned on "just bringing the things I've learned at the local and county level up to the state level."
McGarrigle said his county government record includes working to keep two refineries open, supporting the development of PPL Park in Chester, and establishing a heroin task force.
McGarrigle also wants to focus on education funding and said he would push for greater local control of school district funds.
"There's just too much inequities, the way the money goes up to Harrisburg," he said.
McGarrigle, 54, was elected to the council in 2007.
Erickson, who has served in the Senate since 2001, announced last year that he would not seek reelection. He is supporting McGarrigle and was present at his announcement Monday.
The 26th District includes parts of Delaware and Chester Counties. The Delaware County Republican Party endorsed McGarrigle last month.
John Kane, business manager of Plumbers' Union Local 690, is the only Democrat who has announced a bid for the seat.