Composer of the first modinha to open the genre to systematic recording, "Luar de Paquetá" (recorded by Baiano), Freire Júnior also wrote and enacted 172 musical plays, including operettas, burlettas, and others, possibly becoming the biggest author of Brazilian musical revues. He wrote more than 125 songs, among them the tango-fado "À Beira-Mar" (lyrics by Hermes Fontes, 1922), the samba carnavalesco "Ai, Cabocla Bonita" (1922), "Ai, Seu Mé" (with Careca, success of the Carnival of 1922), and many others. His songs were recorded by some of the great singers of his time, like Vicente Celestino, Francisco Alves, and Baiano.
Júnior evidenced talents for popular music when he was still a child. He studied a little piano and played by ear. At 14, he wrote his first songs. He started then to rehearse a small company of amateur actors, where he launched his composition "O Primo da Califórnia," playing the piano himself. The audition was attended by Chiquinha Gonzaga herself, who encouraged him to pursue music as a career. Freire Júnior then took conductor Agnelo França (professor of the Escola Nacional de Música) as teacher. Júnior continued to write scores for amateur companies, with Joraci Camargo debuting as an actor, still as a boy, in one of them. In 1908, he graduated as a dentist and joined the Justice department, where he would stay until his retirement. In 1913, his "Choro do Malaquias" was recorded by the Grupo do Malaquias, through Odeon. In 1915, Eduardo das Neves recorded his "Jongo dos Pretos" and in 1916, the Banda Odeon recorded his polca "Ai, Ai, Vidinha."
In 1917, he debuted as a composer for a professional theater, writing the score for the revue Tudo Dança (Alvarenga Fonseca/J. Miranda). Two years later, Júnior debuted as an author with the burletta Flor do Mal, writing the music as well. He then presented several burlettas, always with success, especially those released by the Alda Garrido company. "Ai, Amor," written for the revue Reco Reco (Carlos Bittencourt/Cardoso de Meneses), was a big hit in the 1921 Carnival. In the same year, he wrote the marchinha "Ai, Seu Mé" (together with Luís Nunes Sampaio, the Careca). The tune satirized the republic president Artur Bernardes and was signed by Freire Júnior under the pseudonym Canalha da Rua. Even then he was arrested two or three times, being taken to the solitary confinement. That didn't prevent the song from becoming the most sung in the Carnival of 1922, achieving remarkable success. With his friend Hermes Fontes (who wrote the lyrics), Júnior composed one of the most successful modinhas of the period, the one that broke in the recording business, "Luar de Paquetá," opening the way for many others which would be systematically recorded from then on. "À Beira-Mar" (with Hermes Fontes) was recorded by Vicente Celestino in 1922. In the next year, his "Não Olhe Assim," taken from his revue Luar de Paquetá, was recorded by Baiano, with success.
In 1926, Júnior became the director of the recording company Odeon and was in some way responsible for the launching of Francisco Alves, who's 1919 opening at the Popular company went completely unnoticed. His modinha "Malandrinha" was recorded in 1927 by Pedro Celestino, but achieved real success in the next year, in Francisco Alves' recording. In 1928, he had hits with "Samba de Verdade" (recorded by Francisco Alves) and the canção "Santa" (recorded by Vicente Celestino). In 1929, he had success with the political march "Seu Julinho Vem," recorded by Francisco Alves, who also had hits with Freire Júnior's modinha "Deusa" (1931) and the canção "Pálida Morena" (1933). From 1934 to 1939, Júnior became impresario at the Teatro Recreio. In 1936, he took the direction of the comic theater of the Pascoal Segreto Company. He later directed other companies, like Beatriz Costa's, Oscarito's, and Ferreira da Silva's. In 1944, he became the production director of the Company Valter Pinto, for which he produced several very successful revues; Eu Quero Sassaricá, which was the top box office of 1951, breaking records of permanence and yielding the Golden Medal of Production to Freire Júnior, deserves mention.