Born in Novo Hamburgo, Rio Grande do Sul, Guilherme joined Santos' youth setup in 2014, from lowly locals Ivoti/Globalfut.
[3] He made his senior debut fifteen days later, coming on as a late substitute for Jonathan Copete in a 1–0 Campeonato Paulista away win against São Paulo.
[4] Guilherme made his Copa Libertadores debut on 15 March 2018, replacing fellow youth graduate Léo Cittadini in a 3–1 win against Nacional at the Pacaembu Stadium.
[5] On 18 November 2018, Guilherme made his Série A debut, starting in a 2–1 loss at América Mineiro, only lasting nine minutes on the field and being replaced by Renato due to an injury.
[7] In November, after only two unused substitute appearances, his loan was cut short until the end of the year, and he subsequently returned to Peixe.