lavender was still in private practice when governor henry bellmon appointed him to fill a vacancy on the oklahoma supreme court in 1965, representing district no. 1. the vacancy was caused by the impeachment of justice n. b. johnson. the next year, he was elected to hold that same seat for a full six-year term, ending in 1972, and he was subsequently reelected in 1972, 1978, 1984, 1990, 1996, and 2002. while on the supreme court, lavender authored an opinion abrogating state sovereign immunity ("vanderpool v. state", 1983).