Although Rainer suffered from a mild form of epilepsy, this did not visibly interfere with his military career.

The position made Rainer and his wife the head of the Austrian court at Milan.

Throughout the 1840s, the political situation worsened to such an extent that in 1847, Klemens von Metternich resurrected his 1817 plans for an Italian chancellery by sending his right-hand man Count Karl Ludwig von Ficquelmont to Milan as acting Chancellor of Lombardy–Venetia to restore the Austrian rule while taking over Northern Italy's administration.

But only a few months later, Ficquelmont was recalled to Vienna to assume the leadership of the Council of war as the Revolutions of 1848 started.

Through his daughter Adelaide, Rainer is an ancestor of the entire royal family of Italy which reigned from 1861 to 1946.