The discovery was made in the car park of Moortown Baptist Church at 9am this morning.
Her death is not thought to be suspicious, but police are keen to speak to anyone who may have seen the woman's movements beforehand.
The body was found inside a Ford Ka parked just off King Lane.
Detective Inspector James Entwistle of Leeds District CID, said: “The death is being treated as non-suspicious and a file is being prepared for the coroner.
“As part of our enquiries I would like to speak to anyone who might have seen a dark-coloured Ford Ka in the church car park today or in the last 24 hours.
“Anyone who can assist or has any other information is asked to contact Leeds District CID on 101 referencing police log 0281 of 28 December 2017.”
The church stated on their Facebook page that a Feast and Fun social event due to be held earlier today had been cancelled due to 'unforeseen circumstances'.