Mario Oliveri was born on 22 January 1944 within the Diocese of Acqui in Campo Ligure, a comune in the Province of Genoa and region of Liguria in Italy.

On 6 October 1990, Oliveri was appointed the Bishop of Albenga-Imperia by Pope John Paul II; he succeeded Alessandro Piazza, who resigned due to his age.

Following the investigation, the Pope decided to appoint Guglielmo Borghetti as coadjutor bishop of the diocese in January 2015, vesting him with full authority.

[2] The Holy See objected to lack of discernment in the ordination of priests and the willingness to accommodate expelled seminarians from other dioceses previously involved in scandals or considered unfit for the priesthood.

[6] With full episcopal and administrative authority resting in the new coadjutor as of 25 March 2015, Oliveri retained the title of Bishop of Albenga-Imperia without any power.