(idiomatic) Possessing or characterized by robust lungs and a strong voice suitable for loud, sustained public speaking, shouting, wailing, singing, etc.
Example: 1918, B. M. Bower, Cabin Fever, ch. 11:
He would like to know how she was getting alongâ€”and the baby, too. . . . It was a leather-lunged, red-faced, squirming little mite.
1980, Raven I. McDavid Jr., American English: Essays, ISBN 9780804709828, p. 313:
One of the notable effects of technical change has been the obsolescence of leather-lunged oratory of the William Jennings Bryan school, in favor of the "fireside chat" of Franklin Roosevelt; with electrical amplification, a speaker could use conversational style and still be understood in a large auditorium.
2007, James Poniewozik, "Why American Idol Keeps Soaring," Time, 4 April:
Some make a story arc of their performances, like Clarkson, who grew over Season 1 from wallflower to leather-lunged sensation.