Born in Bradford, Pennsylvania, he graduated from Penn Manor High School. He attended the College of William and Mary from 1960 to 1961 and received his B.S. from Millersville University of Pennsylvania in 1964. Walker taught high school from 1964 to 1967. He took his M.A. from the University of Delaware in 1968 and served in the Pennsylvania National Guard from 1967 to 1973.

He became an assistant to Pennsylvania congressman Edwin Duing Eshleman, working for him from 1967 to Eshleman's retirement in 1977. Walker was elected to his seat representing southeastern Pennsylvania, including Lebanon, Lancaster, and Chester Counties.

In Congress, Walker was an outspoken conservative and allied himself with fellow conservatives Newt Gingrich, Robert K. Dornan and Trent Lott and the Conservative Opportunity Society. Michael Barone and Grant Ujifusa wrote that Walker was "scrappy, good humored, and ready to push his principles forward even at the cost of being mocked." He was a hawk on deficit spending and worked to reduce government spending but at the same time served on the science committee and advocated more spending on the space program, weather research, hydrogen research, and earthquake programs as well as pushing for a cabinet-level department of science.

Walker was also responsible for a rare punishment of the Speaker of the House and aiding in the rise of Gingrich. When C-SPAN began televising the House, Walker, Gingrich, and other conservatives found they could reach a national audience with special order speeches, given at the end of the day after the House finished its legislative program. In these speeches, they assailed the Democrats and their leadership in the House. On May 10, 1984, Walker gave one such fiery oration that irritated Speaker Tip O'Neill because the cameras did not show Walker was speaking to a deserted chamber. O'Neill ordered Representative Charlie Rose, whose committee oversaw television coverage, to have the cameras pan the chamber and show Walker and his allies were talking to nobody. No notice of this change was given to the Republicans when it was implemented on May 14, 1984. When the Republicans found out what was going on, Walker, who was speaking when the panning began, and Robert H. Michel, the Republican leader, angrily complained on the floor. The next day, Gingrich was speaking and Speaker O'Neill lost his cool, resulting in O'Neill's words being taken down and ruled out of order. No Speaker had been so punished since 1795. These events made Gingrich a household name. Gingrich would later bring Walker into the Republican leadership; Walker was chief deputy whip.

Walker was a fierce advocate of stronger drug laws. He proposed that all federal contractors institute programs among their employees with violations to result in the forfeiture of federal contracts--even if as little as one joint were found in a contractor's workplace. Walker also led a campaign against the rewriting of the Congressional Record and had the practice banned in the 104th Congress when Republicans won control of the House.

Congressional Quarterly would write that "he has raised too many hackles and rubbed too many nerves to be very popular" in the House, but the voters back in Pennsylvania only once gave him less than seventy percent of the vote.

His name had been circulated as a possible NASA administrator following the 2004 resignation of Sean O'Keefe.