A federal tax filing reveals that the troubled actor-director made the large lump sum donation earlier this year to his Holy Family Catholic Church, which is situated in the secluded Agoura Hills.
The private church now has $37 million in its coffers - up from $27 million last year, according to the tax document.
Gibson's secretive sect is not recognised by the Roman Catholic Church because it does not acknowledge the authority of the Pope or the Vatican and rejects the universally accepted teachings of the Second Vatican Council.
The church - which offers a daily morning mass in Latin - follows an antiquated ideology of Catholicism dating back to the 16th century.
Female followers of Gibson's church must abide by a strict dress code, requiring them to wear veils over their hair and long skirts, with a ban on pants for women.
The exclusive parish currently caters for about 70 families, with the existing chapel having seating for only 100 people.
However, the new church, located 400m up the hill from the current building, will seat about 400 when it is completed in the next 12 months.
Visible throughout much of the valley it overlooks, the high-ceilinged church is being constructed in the architectural style of an old-fashioned Spanish mission.
It is understood that Gibson, 51, also owns the construction company that is building his new place of worship.
Planning documents, seen by The Daily Telegraph, reveal that the current church building will become a meeting hall for the parish.
Gibson and his wife Robyn are listed in federal tax records as directors of the church.
It is run out of Gibson's Icon Production company offices in the beachside suburb of Santa Monica, with an Icon employee responsible for book-keeping.
The Gibsons' tax-free donations to Holy Family are made possible by a charity they established called the AP Reilly Foundation, which operates the church and was named after his late mother, Anne Reilly-Gibson.
The foundation was created in October 1999 for the sole purpose of creating the church.
The church has an unlisted phone number, keeps its address a secret and has asked members of the congregation not to release the information.
The 4.5ha property - located on the scenic and quiet Mulholland Highway - is listed in public documents as being owned by Gibson's foundation and being worth about $3.7 million.
The fenced property is guarded by security and access to the church decided by a staff member at the gate.
Inside, the church is spare and simple, with a very basic altar, exposed wooden beams in the ceiling, dark carpeting, a large iron light fixture and chairs upholstered in maroon fabric.
Discreet video cameras cover the building, surrounded by al Tuscan-style garden of poplars and olive trees.
The church was the venue for the wedding of Gibson's only daughter Hannah, who was walked down the aisle by her father in a private ceremony - reportedly conducted entirely in Latin - last September.
Yesterday, several middle-aged women wearing long skirts, prim blouses, flat shoes and lace veils were wandering the church grounds.
Icon Productions is at present languishing, with nothing in production and one B-movie to distribute.