Police officers and sniffer dogs were in the grounds of the abbey ahead of the service, which lasted about 90 minutes.
The private requiem mass included a homily from the Rt Rev David Charlesworth, Abbot of Buckfast.
He said: “In the midst of the shock, clamour and sometimes unwarranted comment surrounding her death, our response is to pray for the repose of her soul, to give thanks for her fortitude, and offer Holy Mass in this Abbey Church which Ann called her safe haven.”
A statement from the Abbey Church earlier said Widdecombe would be “missed and fondly remembered” and “many in our worshipping community knew her as a kind and warm character”.
“Ann was a woman of profound faith, a faith which found expression in the public forum of politics,” it said.
It added: “Ann was unafraid to express her unwavering convictions, formed through her Roman Catholic faith. She had a sharp intellect and was a dedicated public servant.”
The order of service also included tributes paid by the Rev Roger Widdecombe, Widdecombe’s nephew, and Sir Christian Sweeting, a close friend.
A public memorial for Widdecombe is due to be held later this year.
