But it also served to underline the ongoing threat Temer faces in the multibillion-dollar scandal centered on state oil company Petrobras.
Oliveira, a powerful figure in Temer's PMDB party, replaces fellow party member Renan Calheiros, who steps down after being charged with corruption in the Petrobras case.
However, Oliveira could eventually face charges himself.
In a plea bargain, a former executive for construction firm Odebrecht -- which has admitted to paying fat bribes to land inflated Petrobras contracts -- named him as one of the politicians involved in the scheme, according to Brazilian media reports.
A source close to Odebrecht confirmed the reports to AFP.
Oliveira, 64, is a senator for the state of Ceara, in Brazil's impoverished northeast.
He runs a small agribusiness empire and also a security and logistics firm that has recently won hefty federal contracts, according to the newspaper Estado de Sao Paulo.
In his 2014 financial statement, he declared assets of 99 million reals ($31 million) -- triple what he declared when he was elected to the Senate three years earlier.
Calheiros, who successfully battled finish his term as speaker after being caught up in a dozen graft investigations, now takes over Oliviera's old job as PMDB leader in the Senate.