He served as rector of the diocesan seminary from 1992 to 1994, and in 1997, he was appointed vicar general of the Diocese of Arezzo-Cortona-Sansepolcro and was confirmed in the position in 1999 by the new bishop, Gualtiero Bassetti.

[1] On 17 November 2001, Agostinelli was appointed the Bishop of Grosseto, and received his episcopal consecration from Pope John Paul II on 6 January 2002 in St. Peter's Basilica, with Cardinals Leonardo Sandri and Robert Sarah acting as co-consecrators.

At the meeting, Aurelio Mancuso, the national president of Arcigay, was present along with numerous journalists.

[4] Agostinelli continued to demonstrate openness to dialogue with homosexual communities, meeting with other organizations over the years.

On 29 September 2012, he was appointed the Bishop of Prato by Pope Benedict XVI and was installed in the diocese on 25 November 2013.