Judge Manning was appointed to the bench by Governor Mark Dayton, after being recommended by the Minnesota Judicial Selection Commission. He has served since February 2014 and is currently assigned to a rotation in Juvenile Court. He is presently the longest serving judge in that division. In 2021, the nation's largest foundation working in child protection, Casey Family Programs, named Judge Manning as one of the recipients of its Casey Excellence for Children Leadership awards. In his current assignment, he handles civil child protection matters, juvenile delinquency cases, adoptions, firearm-rights restoration petitions, and expungement requests for juvenile records. Judge Manning previously was assigned to a civil block, where he also handled misdemeanor and gross misdemeanor criminal cases for the western suburbs in the Ridgedale courthouse. Before that, he served on the downtown criminal team.

Before taking the bench, Judge Manning was a partner at a major Minneapolis-based firm, where he worked on civil and criminal matters. As a lawyer in private practice, he worked on cases worth a few thousand dollars to cases worth hundreds of millions of dollars, for plaintiffs and for defendants. On a volunteer basis, he represented children, guardians ad litem, and an inmate with a low IQ who had an unconstitutional death sentence, as well as teaching a course as an adjunct at St. Thomas Law School. He also served as counsel to Minnesotans United for All Families and Project 515.