Saint John's High School is a private Catholic boys' high school located in Shrewsbury, Massachusetts. It is located in the Roman Catholic Diocese of Worcester. The school was founded and is currently sponsored by the Xaverian Brothers.

The Xaverian Brothers' association with Worcester dates back to September 1893, when a pioneer community of four Xaverians arrived in the city to formally open Saint John's Parish Grammar School for Boys. In 1898 a three-year high school curriculum was introduced. A fourth, or senior year, was added in 1906, when the College of the Holy Cross dropped that institution's college prep or high school senior course to concentrate solely on college-level work.

In November 1953, John Cardinal Wright, who was then Bishop of Worcester, transferred the high school property under the new title of Saint John's Preparatory School of Worcester to the Xaverian Brothers. The school population in 1954 consisted of eleven Brothers and 354 students. The brothers purchased a large acre estate in neighboring Shrewsbury. This acquisition was the first step in the expansion of Saint John's to a regional high school serving all of Worcester County. In 1959, one hundred twenty-five acres at the foot of Main Street hill were purchased, and Pioneer Field came into being. In 1962, all classes had transferred to the Shrewsbury location. A gym and cafeteria were added in 1963 and 1964.

In July 2019, Saint John's High School released a statement detailing six Xaverian Brothers, along with one from another order, who sexually abused underage school children—including two offenses on school grounds—and were employed by the school. These were detailed in a report compiled by a former FBI agent.

St. John's has 16 varsity men's sports. In the fall, they compete in football, soccer, golf, and cross country. They also have a club rowing team in the fall. In the winter, they compete in swimming, basketball, wrestling, hockey, alpine ski, and indoor track and field. In the spring, they compete in rowing, lacrosse, baseball, and outdoor track and field.

St. John's has had several alumni play professionally in the National Football League, National Hockey League, and Major League Baseball.

• Edward M. Augustus Jr. (1983)- Worcester City Manager 2014–Present
• Matthew Beaton (1996) - Massachusetts Secretary of Energy and Environmental Affairs
• Peter Blute (1974) – former member of the United States Congress
• John A. Durkin (1954) - former United States Senator from New Hampshire
• Joseph Early (1951) – former member of the United States Congress
• Dan Grabauskas (1981) - CEO of the Honolulu Authority for Rapid Transportation
• Steve Kerrigan - candidate for Lt. Governor of Massachusetts, 2012 CEO of Democratic National Convention, 2013 CEO of Presidential Inaugural Committee
• Tim Murray (1986) – former Lieutenant Governor of Massachusetts
• John F. Smith Jr. (1956) – former CEO/Chairman General Motors
• Mike Birbiglia (attended for one year) – comedian, actor, and NPR contributor; wrote about his freshman year at St. John's in his book Sleepwalk With Me: and Other Painfully True Stories
• John Dufresne (1965) – author and university professor; winner of a Guggenheim Fellowship
• Jim Ford (2000) – Film and television actor, stuntman, screenwriter and film director; stunt double for Edward Norton
• Brett Murphy (2010) – child actor in Fever Pitch and Pulitzer Prize finalist journalist
• Frank O'Hara (1943) – Museum of Modern Art curator; Poet, Meditations in an Emergency, which was featured in Mad Men (there is an episode in season 2 of the television series Mad Men named after the book)
• Andrew J. Olmsted (1988) – U.S. Army major and Iraq War correspondent
• Charlie Pierce (1971) – lead political blogger for Esquire; sportswriter and columnist for the Boston Globe, the New York Times, the Los Angeles Times, the Chicago Tribune, GQ, Sports Illustrated, and formerly ESPN's Grantland; regular contributor to NPR programs Wait Wait...Don't Tell Me! and formerly Only A Game
• Michael Ritchie (1975) – Artistic Director, Los Angeles Center Theatre Group

• John Andreoli (1978) - played for USFL Boston/New Orleans Breakers
• Rob Blanchflower (2009) - tight end for Pittsburgh Steelers, 2014–15
• Sean Burke (2018) - pitcher for Chicago White Sox
• Richard Rodgers II (2011) - tight end for the Los Angeles Chargers with 15 career touchdowns in the NFL. On December 3, 2015, Rodgers caught the longest game-winning, game-ending Hail Mary in NFL history, according to the Elias Sports Bureau.
• Rob Hennigan (2000) - Vice President of Basketball Operations for the Oklahoma City Thunder, former General Manager for the Orlando Magic 2012-17
• Tom Moore (1983) – Quinnipiac University head men's basketball coach, 2007–17
• Brian Abraham - Director, Minor League Operations for the Boston Red Sox; bullpen catcher for the 2013 World Series champion Boston Red Sox
• John Andreoli (2008) - former outfielder for the San Diego Padres, Seattle Mariners, and Baltimore Orioles
• Pat Bourque (1965) – former first baseman for the Oakland Athletics, Chicago Cubs, and Minnesota Twins; 1973 World Series champion
• Ron Darling (1978) – broadcaster; former MLB All-Star pitcher for the New York Mets, Montreal Expos, and Oakland Athletics; Gold Glove winner, 1986 World Series champion, and inductee in the New York Mets Hall of Fame
• Tim Lahey (2000) – Phantom ballplayer, was on the Philadelphia Phillies active roster, but never appeared in a game
• Ryan O'Rourke (2006) - former pitcher for the Minnesota Twins and New York Mets
• Lance Zawadzki (2003) – former shortstop for the San Diego Padres; hitting coach for the Double-A Portland Sea Dogs
• Fran Quinn (1983) - PGA golfer with 8 professional wins
• Jim Stewart (1974) - former goaltender for the Boston Bruins

• Fred Borchelt, former Olympic rower, silver medalist at the 1984 Summer Olympics

• School website