Jenison was born on 20 January 1732 in Edinburgh, Scotland, and was baptised into a prominent English Catholic family at Heighington in County Durham.
[1] His brothers John and James both became a Jesuit priests and Francis inherited the family estate.
He sold the family estate, Low Walworth, and retired to the continent, settling in Heidelberg in 1775 where he became Chamberlain to the Elector Palatine Prince Charles Theodore (who also became Elector of Bavaria in 1777 upon the death of his 12th cousin, once removed, Prince Maximilian III Joseph).
Together, they lived in the family mansion at Low Walworth and were the parents of:[5] Count von Jenison died in Heidelberg on 30 June 1799.
[6] Through Franz's second marriage, he was a grandfather of another two boys, only one who survived to adulthood, and four girls, the youngest of whom was Countess Emilie (or Amelia) von Jenison-Walworth, from whom descended the princes of Löwenstein-Wertheim-Freudenberg, and through them, other German royalty.