[6] In 2010, on the recommendation of Lloyd A. Karmeier, the Illinois Supreme Court appointed McGlynn to a judgeship in the 20th Judicial Circuit to succeed Michael O’ Malley, who retired to return to private practice.

[7] In 2012, McGlynn ran unsuccessfully to again serve on the Illinois Appellate Court, narrowly losing to Democrat Judy Cates.

The Illinois Supreme Court appointed L. Dominic Kujawa Jr. to the vacancy created by McGlynn's elevation to the federal bench.

President Trump nominated him to the seat vacated by Judge Michael Joseph Reagan, who retired on March 31, 2019.

[18] In November 2024, McGlynn held that the Protect Illinois Communities Act, a 2023 law banning assault rifles, large capacity magazines, and other gun accessories, was unconstitutional under the Second Amendment.