Caccia was born in Milan but lived for many years in [[Cavaria con Premezzo]]. He was ordained a priest on 11 June 1983 by Cardinal [[Carlo Maria Martini]] and served in St. Giovanni Bosco parish in [[Milan]] until 1986. ThenHe he was sent toattended the [[Pontifical Ecclesiastical Academy]] in [[Rome]], where heand obtained a [[Doctor of Sacred Theology|Doctorate in Sacred Theology]] (S.T.D.) and a [[Licentiate of Canon Law]] (J.C.L.) from the [[Pontifical Gregorian University]]. He joined the diplomatic service of the [[Holy See]] on 1 July 1991<ref name=vatbio/> and was appointed an [[attaché]] in the [[Apostolic Nunciature]] in [[Tanzania]].<ref>{{cite news |work= Zenit| url = http://www.zenit.org/it/articles/il-papa-invia-un-suo-stretto-collaboratore-come-nunzio-in-libano |title=The Pope sends his close associate as Nuncio in Lebanon |access-date = 16 November 2019 | date= 16 July 2009| language = it }}</ref>
On 11 June 1993 he returned to Rome to work in the General Affairs Section of the [[Vatican Secretariat of State]]. On 17 December 2002 he was appointed Assessor for General Affairs of the Secretariat of State where he worked under Archbishop [[Leonardo Sandri]] and, after 2007, Archbishop [[Fernando Filoni]].
