The New York Yankees hired Stewart as a scout in 1953. He was trained by legendary Yankee scout Lou Maguolo. He scouted, suggested and signed many players for the Yankees. Working mainly in the Midwest, the first player Stewart discovered and steered to the Yankees was pitcher Jim Bouton, who had not attracted any interest from Major League teams while in high school. Bouton became a starting pitcher for the Yankees in the early 1960s.
Stewart has served in multiple roles for the Kansas City Royals since joining the MLB expansion franchise in 1969. In 1985, Stewart he was Director of Scouting. In 1986, he was both Scouting Director and Player Development. From 1987 to 1997, he served as only Scouting Director. The next two years, from 1998 to 1999, Stewart became the Senior Special Assistant to General Manager. From 2001 to 2005, Stewart became the Senior Advisor to the General Manager, and continues in that position in 2015.
Stewart is the longest tenured Kansas City Royals associate and he was inducted into the Kansas City Royals Baseball Hall of Fame during 2008 season, on June 28. Stewart represented the Kansas City Royals Hall of Fame class of 2008, becoming the 23rd member of the elite group. Stewart is the Royals' Senior Advisor to General Manager (GM) Dayton Moore. Seventy players that Stewart drafted have played Major League Baseball. They include Bo Jackson, Kevin Appier, Brian McRae, Mike Sweeney, Johnny Damon, Joe Randa and Carlos Beltran. He co-authored a book, The Art of Scouting, with Kansas City newspaper writer Sam Mellinger in 2014.
In an interview with Dick Kaegel of MLB.com on Oct. 17, 2014, as the Royals advanced to their first World Series appearance since 1985, Stewart told a story from his Chicago childhood: "When I was 8 or 9 years old, playing ball as a kid, my mother said, 'You know, you're going to be in professional baseball someday.' I said, 'What do you mean, Mom?' She said, 'Because you were born on Feb. 6, Babe Ruth's birthday, in 1927, the same year that he hit 60 home runs.' She was right. Talk about scouting!"
- "Art Stewart Royals Hall of Fame induction ceremony set for June 28". MLB.com. Retrieved 2008-08-10.
- Posnanski, Joe (2001). The Good Stuff: Columns about the Magic of Sports. Kansas City, MO: Kansas City Star Books.
- "Titles of Art Stewart". www.baseballamerica.com. Retrieved 2008-08-10.
- "Art Stewart selected to Royals Hall of Fame". MLB.com. Retrieved 2008-08-05.
- "Royals Hall of Fame Class of 2008: Art Stewart". royals.mlblogs.com. Retrieved 2008-08-06.