He was a general attorney of the Federal Trade Commission, Division of Compliance, Bureau of Deceptive Practices from 1969 to 1970. He was in private practice in Ardmore, Oklahoma from 1970 to 1994.
On January 14, 2014, Kern held that the Oklahoma Constitution's definition of marriage as limited to "the union of one man and one woman" violates the Equal Protection Clause of the Fourteenth Amendment. The suit, Bishop v. Oklahoma, had been filed by two lesbian couples against the Tulsa County Clerk and others. The ruling has been stayed pending appeal.[2] The amendment banning same-sex marriage was passed by the voters in 2004, and its legislative history was cited in the ruling.[3]