Jorge Messias has served in a role equivalent to Brazil's minister of justice since 2023, and is a close advisor to Lula. 34 senators voted for him, while 42 voted against. He needed 41 votes to be approved.
It is the first time since 1894 that Brazil's Senate has blocked a nominee to the Supreme Court.
Lula nominated Messias to replace Luís Roberto Barroso, who resigned in November. Since then, the court has operated with only ten members.
Lula hopes to be re-elected for a fourth term in October. His challengers include Flavio Bolsonaro, son of former President Jair Bolsonaro.
