He played in Major League Baseball (MLB) as a right-handed pitcher for the Kansas City / Oakland Athletics, Washington Senators, Seattle Pilots, St. Louis Cardinals, Boston Red Sox.

[2] On December 7, 1973, he was traded by St. Louis along with Reggie Cleveland and Terry Hughes to the Red Sox in exchange for John Curtis, Lynn McGlothen and Mike Garman.

[3] Seguí holds the unique distinction of having pitched for both of Seattle's major league baseball teams, the Pilots and the Mariners, in the first game ever played by each franchise.

[2] Seguí continued pitching in the Mexican League for another 10 years, tossing a no-hitter for the Cafeteros de Córdoba during the 1978 season.

[8] He also gained induction into the Hispanic Heritage Baseball Museum Hall of Fame on August 19, 2006, in San Francisco, California.