[3] In 1971, following the resignation of Morell Edward Sharp, Evans appointed Utter to the Washington Supreme Court; he was sworn in on December 20, 1971, at the age of 41.

[1][4] That year, he was criticized by members of the Washington State Prosecuting Attorneys' Association as being overly "soft on crime".

The prosecutors felt that Utter was too quick to throw court cases out on technicalities, letting "criminals go free".

[2][6] Utter's tenure was characterized by support of free speech and freedom of religion, funding education, the environment, social services, and youth programs.

[1] He also defended the “criteria approach” used by the supreme court in assessing states rights issues that conflicted with federal laws.

[12] On March 30, 1995, Utter wrote a letter to Governor Mike Lowry announcing that he was resigning from the court in protest of the death penalty, effective on April 24, 1995.

[1][7] In 1997, Utter led a task force in King County that resulted in the establishment of therapeutic courts, focused on mental health.

[2][3][18] Utter traveled around the world after working to help developing nations create independent judiciaries and was a member of the American Bar Association's Central European & Eurasian Law Initiative.

With the American Bar Association's initiative, he taught about judiciary in Albania, advised Mongolia and Moldova, and was asked to help set up a constitutional court in Sarajevo.

"[21] After Governor Jay Inslee imposed a moratorium on state executions in 2014, Utter described it as an "overwhelming relief", saying that "all the past effort had not been wasted.

[2] In 2016, Robert F. Williams wrote that "Taken together, Justice Utter's academic writings could have formed the basis for an influential book that would still be useful today in Washington and across the country."

Charles W. Johnson said that "Utter's development of an independent interpretation of the State Constitution was probably as strong an influence on this court as could have been achieved by any individual".

[2] The "Robert F. Utter Award" is presented to individuals who "show consistent, outstanding and sustained contributions to the cause of civic leadership in Washington."