She graduated from Stephens College and then the University of Missouri.
She has four children. Pekelis was appointed to the King County Superior Court by Dixy Lee Ray, and later re-elected to that position. While there, she was widely noted for a humorous incident in which she asked a police officer in her court who was chewing gum to throw it away.
The officer misunderstood her and began to place his gun in the wastebasket.
Booth Gardner appointed Pekelis to the Washington Court of Appeals, a position to which she was also later re-elected. In total, she served on that court for nine years.
Pekelis was appointed to the Washington Supreme Court by Mike Lowry in April 1995 to fill a seat left empty by the departure of Bob Utter. Major cases of hers include a 1992 Court of Appeals ruling that gender-based peremptory challenges violated the Equal Rights Amendment to the Washington Constitution as well as the United States Constitution, as well as a 1995 Supreme Court ruling for the adequacy of existing implied consent warnings given to drunken driving suspects before they took breathalyzer tests.
In her re-election race in November 1995, Pekelis faced Richard B. Sanders, a local land use attorney.
Sanders defeated her in the election by about 53% to 47%. Seattle Times columnist Terry Tang decried Sanders" campaign as "boorishly partisan" and wrote that the departure of "an excellent judge like Rosselle Pekelis" would likely fuel further distrust of the judiciary. The race was later analysed as the start of a trend towards increasing politicization of judicial elections.
After her election defeat, Pekelis would go on to join the Seattle Ethics and Elections Commission in 1996 and form a mediation firm with other former area judges in 1997.