Born in Burley, Idaho on February 4, 1963, Grigg graduated from Utah State University, majoring in political science. He served as Provo Daily Herald columnist and Washington journalist before "seeing the light" and starting work in 1993 as a correspondent, researcher, and senior editor for The New American, the official biweekly magazine of the John Birch Society (JBS). Based at the JBS's Appleton, Wisconsin, office, Grigg covered United Nations summits and conferences from 1994 to 2001, and wrote Freedom on the Altar (1995), a study of UN family policy.

Associate Kevin Bearly, a minister and former police officer, conducted JBS summer youth camps in the 1990s at which Grigg and others promoted conservative causes. Grigg has also spoken frequently on conspiracies and Clinton impeachment in Las Vegas, Colorado Springs, and Salt Lake City. Grigg was associate director for Activate Congress To Improve Our Nation (ACTION), a committee incorporated by JBS to promote the impeachment of President Bill Clinton, with chapters in 50 states.

In 2005, Grigg called for the resignation of the JBS president and CEO, G. Vance Smith, who had promoted two sons to leadership positions; Smith was narrowly deposed in a September 2005 Board of Incorporators vote. The new CEO, Arthur R. Thompson, and other leaders initiated a staff blog to which Grigg contributed heavily.

Grigg's writing reflects views heavily influenced by Constitutionalism, libertarianism, and anti-communism; Ward Churchill favorably quoted Grigg's observation that totalitarianism is defined by abundance and unintelligibility of laws. While Grigg's polemical style in print and blogs has been termed "verbal pugilism", The New American uses a modified AP Stylebook, avoiding overuse of emotional or satirical terms. Grigg is also younger than the other senior JBS officials. Grigg's articles as edited and accepted for publication by The New American have been regarded as less emotionally charged than those he has submitted to other publications; he has written for LewRockwell.com since June 2004, and has contributed increasingly to The American Conservative.

The new JBS leadership launched the U.S. immigration issue as a major campaign in 2005. Grigg, of Mexican and Irish descent, had often in JBS publications called for controls on immigration. His New American article "Revolution in America", a study of immigration problems and issues, was reprinted for its "current and incisive" rhetorical qualities by a McGraw-Hill college text. Grigg has promoted the concept that "white Leninists" desired to send "millions of Mexicans across the border with the idea of having each kill 10 Americans".

But by 2006 Grigg had decided that the immigration issue had been overplayed by the Republican Party as a driving cause to keep big-government, pro-war Republicans in control of the U.S. Congress. He argued that an attack on personal liberties by the George W. Bush administration and the Republican Party was a more serious impediment to personal liberty, charging the administration with committing torture, detention without trial, warrantless surveillance, and wars of empire. Grigg considered a "wave" of media attention on immigration to be "nothing more than the swirl in the bowl after the chain has been pulled" on the Republican Party.

Grigg formed a personal blog, "Pro Libertate", in August 2006, saying that JBS leadership had deleted some of his posts from their blog, such as a June comparison of immigration debate to professional wrestling. Pro Libertate: Will Grigg's Birch Blog - The Lost Episodes He stated that he was fired by JBS on October 3, 2006, officially for unstated reasons. Pro Libertate: Tonight's Episode: The Tory Perspective, or There Goes my Severance (THIRD UPDATE; see comments section)

The Robert W. Welch Foundation (Right Source Online), founded in 1997 by former California JBS members, adopted Grigg's Pro Libertate blog and made him a weekly cohost (December 30, 2005 — May 4, 2007) on the nationally syndicated afternoon radio show "The Right Source" with Kevin Shannon (Bearly's pseudonym). It also launched the Pro Libertate e-zine, where Grigg brought in writers such as James Bovard and fellow LewRockwell.com columnist Scott Horton. It commissioned Grigg's 2007 book alleging Bush and Clinton attacks on liberty, Liberty In Eclipse.

Grigg has recorded the radio spot "A Liberty Minute" weekdays since February 19, 2007, which, since July 2, has used the tagline, "Let us take back the liberty wherewith Christ has made us free" (Galatians 5:1).

Grigg is also a studio musician who served as lead guitarist in the Wisconsin band "Slick Willie and the Calzones" until his 2005 move to Idaho. The band's 2001 CD, Green and Gold, featured rock, country, and jazz homages to the Green Bay Packers, such as the novelty song "Tailgate Polka".

Grigg and his wife Korrin have six children. He cited his wife's 2006 illness as a reason for suspending his secondary guitar activities.