I hardly knew it except from Thurber's story, which if I read, it was so
long ago I've forgotten everything else about it.
Green has some interesting light on it:
"catbird (Dumatella carolinensis), known for its harassing of fellow
birds. The catbird takes up a high, exposed position to deliver its
song. The image is of a cat looking down on a targeted bird. Orig. a
term used by a poker opponent of the sportscaster Red Barber (1908–92)
and popularized first by him and latterly by a James Thurber story, ‘The
Catbird Seat’ (14/11/1942)."
1 (US) a person of authority or power.
1924 W.E. Woodward Lottery 200: He's a catbird, all right. He's a leader
in the advertising field.
1931 W.E. Atkins Economic Behavior 182: Garrison, the ‘Holdfast’ button
king, liked Connelly, said ‘He's a catbird’.
1968 ‘Hy Lit’ Hy Lit's Unbelievable Dict. of Hip Words 8: cat bird – The
main man, the leader, top guy, the boss.
Then comes the "catbird seat", starting with Thurber:
1942 J. Thurber in New Yorker 14 Nov. 17: ‘Sitting in the catbird seat’
meant sitting pretty, like a batter with three balls and no strikes on him.
But the Thurber story itself refers back to Barber (a broadcaster whose
earliest use of the expression appears not to be dated):
[In the Thurber story] "Mrs. Barrows likes to use the phrase. Another
character, Joey Hart, explains that Mrs. Barrows must have picked up the
expression from the baseball broadcaster Red Barber and that to Barber,
"sitting in the catbird seat" meant "'sitting pretty,' like a batter
with three balls and no strikes on him."
https://en.wikipedia.org/wiki/The_Catbird_Seat
Notice that the last is just an example of a situation in which it might
be used, rather than a specific meaning. Elsewhere it is mentioned among
Barber's numerous catchphrases:
"Sittin' in the catbird seat" – used when a player or team was
performing exceptionally well.
https://en.wikipedia.org/wiki/Red_Barber
And later uses are by no means restricted to baseball:
1952 Wall Street Journal 3 June 11: A week of homage to secretaries,
whom a public poll already had indicated are in the catbird's seat at
the business of snaring a spouse.
1958 Wodehouse Cocktail Time 114: ‘I get you. If we swing it, we'll be
sitting pretty,’ ‘In the catbird seat.’
1978 W. Diehl Sharky's Machine 135: You're in the catbird seat there.
1992 R. Price Clockers 575: The first guy comes in voluntarily […] that
guy's gold, that guy's in the catbird seat.
2001 Pittsburgh Business Times 22 Jan. [Internet] Who could blame Mr.
Murphy for being a little giddy at the opportunity to sit in the catbird
seat for a change.
Though there is always the possibility of a play with a literal seat of
some kind:
1953 Mad mag. Jan.–Feb. 19: He'll be riding in the cat-bird seat of the
emperor's chariot
1962 T. Berger Reinhart in Love (1963) 152: He led Reinhart to his own
swivel chair and forced him into it. ‘How do you feel in the catbird
seat, boy?’
Nevertheless the origin of this expression does not seem to owe anything
to a particular seat in a motor vehicle.
https://en.wikipedia.org/wiki/Catbird_seat