May 8, 1995 for the Oakland Athletics against the Texas Rangers in Oakland. Jason was the DH and came to the plate 5 times getting 1 hit and 1 walk in an Athletics 7-4 loss.
Jason Varitek
Jason Jennings
The first major league, the National Association, started in 1871. The National League's first year was 1876 and the American League's first year was 1901.
Jackie Robinson's first major league team was the Brooklyn Dodgers.
If you do not count the Negro League, the first non-white major league player was the great Jackie Robinson.
first to play
The main MLB team that Jason Giambi played for professionally is the Oakland Athletics. Another of the teams that Jason Giambi played for is the Colorado Rockies.
The first major league in baseball was the National Association whose first year was 1871.
Emmett Ashford is the first black umpire in a major league game when Cleveland beats Washington
Jason Varitek caught four no hitters, which is an MLB record for a catcher.
Although the definition of "major league" has been argued, present day MLB, as well as the Hall of Fame, define the first "major" league as the National League founded in 1876. The link below describes the first game played in that league, on April 22, and mentions that Jim O'Rourke got the first hit in that game.
Because the National League has been in existence longer than the American League ... the National League's first season as a major league was 1876 and the American League's first season as a major league was 1901.