Judge Zimmer retired from the Iowa Court of Appeals in September 2008, where he had served since 1999. He presently serves the court as a Senior Judge.
Judge Zimmer attended the University of Iowa where he received his bachelor's degree in 1969 and law degree in 1972. After graduating from law school, Judge Zimmer served as an officer in the United States Army. After completing his tour of duty in 1973, he served as an assistant county attorney for Linn County and an adjunct college instructor. Judge Zimmer later served as an area prosecutor for the Iowa Attorney General's Office and as an Assistant United States Attorney for the Northern District of Iowa. He was a member of the Mossman Law Firm in Vinton before his appointment to the bench as a district court judge in 1985. Judge Zimmer served as a judge in the sixth judicial district for 13 years before his appointment to the Court of Appeals. Judge Zimmer served as co-chair of the Bench-Bar Committee of the Iowa State Bar Association. He served as faculty for the Judicial Department's New Judge Orientation Program since 1992. He received the Award of Merit from the Iowa Judges Association in 2004.