After graduating high school in the Denver area, Bates joined the United States Marine Corps in 1959, and served in the Corps until 1963. Relocating to San Diego, Bates became a banker and later a businessman in the aerospace industry.

Bates was elected to the San Diego city council in 1971. While serving he obtained his masters degree from San Diego State University. He was elected chairman of the San Diego County board of supervisors in 1974, and held the position until 1982.

Bates resigned from the board to run for a seat in the U.S. House of Representatives, representing California's newly created 44th Congressional District. His district was created after the 1980 census round of redistricting as the most Democratic district in the San Diego area (it included much of the territory represented for 18 years by Lionel Van Deerlin before his defeat by Duncan Hunter). He was easily re-elected in 1984, 1986, and 1988.

Bates was accused in October 1988 of making sexual advances toward female members of his staff. Bates scoffed that the accusations were part of a Republican smear campaign, but also apologized for any offense he may have caused to his female staffers. As the story had not developed very far by the time of the election, Bates easily won his 1988 race. But a year later, the House Ethics Committee sent Bates a letter directing him to make formal apologies to all of his staffers who had filed the complaints. His Republican opponent in 1990, Randy "Duke" Cunningham, a naval pilot during the Vietnam War, hammered Bates on the scandal, and defeated Bates by a little more than a point.

Bates attempted a comeback in 1992. His home had been drawn out of his old district and into the newly created 50th District, along with many of the more Democratic areas of the 44th. The new 50th was far more Democratic than the 44th had been when Bates had been in office, and it was widely believed that victory in the Democratic primary would be tantamount to election. He finished third in the Democratic primary, which was won by San Diego Deputy Mayor Bob Filner, one of his former aides (who still holds the seat). Bates hasn't attempted to return to elective office since then.

Ironically, even though Cunningham defeated Bates in 1990 primarily due to Bates' sex scandal, Cunningham pleaded guilty to tax evasion and bribery charges and resigned his office in disgrace in 2005. In March 2006, Cunningham was sentenced to eight years in prison.