He began his professional career at 17 years old as a reporter for the Rio Grande do Sul-based newspaper Zero Hora, where he gained the nickname "Peninha", based on Fethry Duck of the Walt Disney universe.

[7] During this period, Bueno released twelve other works on historical themes including, but not limited to, the Caixa Econômica Federal ("Caixa: Uma História Brasileira"), the Brazilian Health Regulatory Agency ("À Sua Saúde — A Vigilância Sanitária na História do Brasil"),[8] Porto Alegre-based Grêmio FBPA ("Grêmio: Nada Pode Ser Maior"), the Avenida Rio Branco in Rio de Janeiro ("Avenida Rio Branco"), public health in Brazil ("Passado a Limpo"), the Confederação Nacional da Indústria ("Produto Nacional"),[9] and the band Mamonas Assassinas ("Mamonas Assassinas - Blá, Blá, Blá: a Biografia Autorizada").

From September to November 2007, Bueno hosted the series "É muita história" on the show Fantástico, broadcast on Rede Globo.

[12] In 2010, he was interviewed by Steve Kroft of 60 Minutes as part of a segment on Brazil as a growing economic power on the world stage, as well as on president Luiz Inácio Lula da Silva.

[13] Though his works have been used as part of the teaching material of Brazilian classes and Bueno has been at points been viewed as a historian, his education and professional background is in journalism.

[14] When asked about this by Laurentino Gomes, Bueno responded that the discussion increasingly became unnecessary and foolish, and that many historians could immediately differentiate between a historiographical investigation and what he does.