In 1959 he was appointed judge of the Anaheim-Fullerton Municipal Court. President Lyndon B. Johnson appoinyed him to the Federal District Court for the Central District of California in Los Angeles, formed in 1966. He was appointed to the Ninth Circuit in 1979 by President Jimmy Carter.
Notable cases include a 1971 decision after Spencer Haywood was denied a transfer from the American Basketball Association's Denver Rockets to National Basketball Association's Seattle Supersonics. The NBA at the time prohibited college graduates to play for four years after graduation; the ABA did not. The antitrust suit went to the Supreme Court, which affirmed the decision.
His ruling in Sony Corp. of America v. Universal City Studios, Inc. in 1979 ushered in the era of home video recording by allowing Sony to market the Betamax.
Ferguson assumed senior status on the Ninth Circuit in 1986. He died at his home in Fullerton, California.