Roy served in the United States Air Force, 1953-1955, and was discharged with rank of captain. He practiced medicine in Topeka from 1955 to 1970 and was elected as a Democrat to the Ninety-second and Ninety-third Congresses (January 3, 1971-January 3, 1975). He changed his registration in 1970 to run as a Democrat. () He was not a candidate in 1974 for reelection but was an unsuccessful candidate for election to the United States Senate in that year; he lost to Bob Dole only by a few thousand votes. In a 1996 interview with PBS, he explained his decision to seek election to the Senate, saying, "I was far from an admirer of Bob Dole, I'll tell you that. He'd been around and he had been pretty much a hatchet man, both in Kansas, and as far as President Nixon was concerned. And so I saw it as a wonderful opportunity to take him out of politics, which I thought was very important at that time." He ran for the US Senate again in 1978 but lost to Nancy Kassebaum. He resumed the practice of medicine in Topeka until 1989 and is a resident of that city.
Since 1989, Roy has been a regular columnist for the Topeka Capital Journal,Kansas paper of record.. His columns often reflect a liberal perspective, including strong support for universal health insurance and opposition to the policies of President George W. Bush His 2001-2002 columns in the Metro News, a Topeka paper, rallied sentiment to stop the sale of Kansas Blue Cross Blue Shield to Anthem of Indianapolis (now Wellpoint) His column appears on Saturdays.