The identity of the woman, buried in 1787 under the Barfüsser church in Basel, has long been a mystery, the Basler Zeitung reported.
She was discovered 40 years ago during renovation work at the church and known as “the lady of the Barfüsser church”.
But following several years of research, scientists have now revealed that the best preserved mummified remains in Switzerland are those of Anna Catherina Bischoff.
DNA tests show Bischoff died of mercury poisoning, which explains why the remains were so well preserved – the poison acted as a preservative.
It's believed Bischoff was suffering from syphilis, which was at that time treated with mercury.
The pastor's daughter, aged 67 when she died, had seven children one of whom married a Baron Pfeffel of Kriegelstein, a member of Johnson's family tree, the Swiss news agency SDA reported.
The British foreign minister is the six-times grandson of the Basel mummy.