Upon finishing his law studies, he moved to Rio de Janeiro where he became a journalist.
During the 1920s and 1930s he worked for newspapers such as Jornal do Brasil and Correio da Manhã.
He co-founded the newspaper A Manhã; its literary supplement Autores e Livros would become an important publication in Brazilian literature.
Leão wrote more than a dozen books, covering all aspects of literature.
He succeeded Humberto de Campos to the Brazilian Academy of Letters and served that institution in various capacities for several decades.