Born in Tsushima, Nagasaki Prefecture, Japan and raised in Minami-ku, Fukuoka, he played for the Hanshin Tigers in Japan from 1990 until 2000, then for Major League Baseball's New York Mets and San Francisco Giants. In 2002, he became the first Japan-born player to play in the World Series, where he went 1 for 6 with three strikeouts. He ended his three-year stint in American baseball by being demoted to AAA after hitting .193 for the first half of the 2003 season. He returned to Japan and played for the Hokkaido Nippon Ham Fighters from 2004 until 2006. He is known for his flamboyance, colorful wristbands, dyed hair, and a unique hop as he catches the ball. His uniqueness has endeared him to baseball fans and has made him one of the most popular players in the Japanese leagues despite not being in the echelon of elite active players. In fact, his popularity was what kept him off the bench during his stint with the Tigers when manager Katsuya Nomura tried to turn him into a pitcher on the rotation rather than risk his team with his mediocre play.
Shinjo ended his career in storybook fashion. Playing for years on losing teams in Hanshin and despite playing in the 2002 World Series, Shinjo showed emotion and shed tears as his final game crowned him a champion as he was a member of the Fighters squad that won their first Japan Series title since 1962 with a 4 games to 1 series win over the Chunichi Dragons. As Shinjo took the field for the top of the ninth inning in the final game, he was given a standing ovation from the home crowd. Before the inning began, he was visibly emotional. Although the final play was only close to him (left fielderHichori Morimoto caught the final ball) the cameras all showed only Shinjo's dramatic reaction. Traditionally, the players toss the manager in the air for series wins first, but the players tossed Shinjo in the air first instead of manager Trey Hillman.
Shinjo is now a television celebrity in Japan as well as a model for his own line of clothing. He has also won the maximum 10,000,000 JPY prize in a celebrity edition of the Japanese version of "Who Wants to be a Millionaire?".