Green’s Dictionary of Slang

(US) an important or influential situation or position, thus in the big leagues, moving in powerful circles.

1907		T.A. Dorgan in Zwilling TAD Lex. (1993) 18: The National Academy of Design is the ‘big league’ of brush wielders.
1914		R. Lardner You Know Me Al (1984) 52: I will get back in the big league and show them birds something.
1944		D. Burley Orig. Hbk of Harlem Jive 39: You’re batting in the Big League, and scoring every inning.
1947		B. Stiles Serenade to the Big Bird 11: He was in the big league.
1953		‘John Eagle’ Hoodlums (2021) 16: ‘Jeannie’s in the big leagues. She hasn’t dated anyone from the neighborhood’.
1963		(con. 1944) L. Glassop Rats in New Guinea 207: This guy’s talking sense. This guy’s in the big league.
1974		G.F. Newman You Flash Bastard 68: The amounts he had tucked away in his two bent bank accounts didn’t put him in the big league.
1991		M. Myers et al. Wayne’s World [film script] You can either stay in the big leagues and play by the rules . . . Or you can go back to your farm club.