Associate Justice Christopher Dietzen announced Thursday that he plans to step down from the Minnesota Supreme Court this summer.

“The work of a justice has been both challenging and rewarding,” Dietzen said in a statement. “The challenge of deciding difficult cases has been made easier by serving with exceptional colleagues. The reward is in the opportunity to participate in a collaborative decision process.”

Dietzen, 69, is just shy of the state’s mandatory retirement age for judges, which is 70.

Republican Gov. Tim Pawlenty appointed Dietzen to the court in November 2007. Before that, Dietzen joined the Minnesota Court of Appeals in December 2004, also appointed by Pawlenty.

“For more than a decade, Justice Dietzen served our court system admirably, both as a wise and thoughtful jurist, as well as a leader in our efforts to improve the administration of justice in our state,” said Supreme Court Chief Justice Lorie S. Gildea. “As a respected colleague and a true friend, he will be greatly missed.”

Dietzen’s departure will give DFL Gov. Mark Dayton his fifth appointment to the seven-member panel. In a statement, Dayton said he and the Judicial Selection Commission would consider a replacement in the coming months.

“For eight years, Justice Christopher Dietzen has served the people of Minnesota on our state’s Supreme Court with honor and distinction,” Dayton said. “Justice Dietzen’s contributions to justice and jurisprudence will have a lasting impact on our state. On behalf of all Minnesotans, I thank him for his dedicated service.”

Dietzen gave Dayton notice of his retirement in a letter Wednesday, writing that “I have pondered for several months whether I should retire this summer and give the Governor the opportunity to appoint my successor; or, retire at the end of my term in January 2017 and have my successor determined by the November 2016 election.”

He added: “Both options are available under the Minnesota Constitution. My judgment is that having you exercise your constitutional authority to appoint my successor best serves the judicial branch and the citizens of Minnesota.”

Dietzen worked as a campaign lawyer for Pawlenty’s 2002 gubernatorial run and played a key role in defending Pawlenty in a controversy over a political TV ad during that race.

In 2010, in a high-profile case, Dietzen wrote the unanimous ruling upholding the conviction of Michael Zabawa in a murderous rampage at a farmhouse outside of Waseca in 2007.

Dietzen said the Supreme Court benefits from having a diverse set of jurists.

“The strength of the Supreme Court is in the balanced perspective of seven justices who bring different backgrounds and experiences to the process of deciding difficult cases,” Dietzen said. “This collaborative, deliberative process produces decisions that endure the test of time.”

Dietzen also serves as the chairman of the Minnesota Sentencing Guidelines Commission, and is a member of the Minnesota Judicial Council, the policymaking body of the Minnesota judicial branch.

Dietzen has advocated for changes in civil cases procedures to promote the speedy and efficient processing of those cases.

He also has championed the Supreme Court’s traveling oral argument program. The initiative brings state Supreme Court oral arguments in real court cases to high school auditoriums and gymnasiums across the state, allowing thousands of students to get an up close look at the justice system.

Before his public service, Dietzen was a shareholder with the Larkin, Hoffman, Daly and Lindgren law firm in Bloomington, where he was its senior litigator.

A native of Washington state, Dietzen earned his law degree from Gonzaga University School of Law in Spokane in 1973 and his bachelor of business administration from Gonzaga University in 1969.