Leonhard was born in St. Margarethen (Bavaria), District of Rosenheim, the seventh child of Georg Dientzenhofer and Anna Thanner.
His four brothers, Georg, Wolfgang, Christoph and Johann, were also well-known architects/builders.
On 30 January 1685 in Waldsassen, he married Maria Anna Hager, a sister of the wife of his brother Georg.
Soon after the death of his wife Maria (6 July 1699), he married in Bamberg Anna Margaretha Sünder from Staffelstein.
In 1697 he commissioned a reprint (with changed dedication and foreword) of the book Theatrum architecturae civilis by Charles Philippe Dieussart.