In 1922, Pierce ran a successful campaign for governor against incumbent Ben W. Olcott. At the time, the Ku Klux Klan was growing in influence and power across the state, and had drafted the overtly anti-Catholic and anti-semitic Compulsory School Act, a bill to require all school-age children to attend public schools. Governor Olcott defiantly refused to work with the Klan in any way. Pierce tacitly accepted the Klan's endorsement and lent his support to the school bill.
As governor, Pierce was at odds with a Republican-dominated legislature. His administration was able to continue the road-building policies of the previous two administrations, but could not win passage of a state income tax or assessed value license fees for automobiles. He attempted to gain support from progressive Republicans on issues of prison reform, reforestation, and hydroelectric development, but divided the state Democratic Party by endorsing Robert M. La Follette for President in 1924. The Ku Klux Klan, which had endorsed him only a few years earlier, began an unsuccessful recall effort.
The Compulsory Education Act was later struck down by the Supreme Court of the United States in its 1925 Pierce v. Society of Sisters decision, on the grounds that it violated the Fourteenth Amendment to the United States Constitution
He later made it to Congress for one term. He died in his 90's - Salem Oregon.