The pop legend, 61, praised Cyrus, 26, telling her that she was a 'woman who has lived' and 'did not need' to apologise for any previous exploits.
In the Instagram post and series of tweets, Cyrus stated it was 'no secret' she partied, experimented with drugs and previously cheated on her ex boyfriends, but said she remained faithful to Hemsworth, 29, during their relationship.
Cyrus said: 'The truth is, once Liam & I reconciled, I meant it, & I was committed. There are NO secrets to uncover here.'
'You can say I am a twerking, pot smoking , foul mouthed hillbilly but I am not a liar.'
As noted by Instagram account Comments By Celebs, Madonna joined several other celebrities including Victoria’s Secret supermodels Taylor Hill, 23, and Lily Aldridge, 33, and actress Shailene Woodley, 27, in showing support for Cyrus, with Madonna writing: 'Thank God. You are human! A woman has lived. No need to apologise!@
Cyrus has previously stated how she looked up to Madonna as a child, and the pair performed a mash-up of Madonna’s Don’t Tell Me and Cyrus’ We Can’t Stop in 2014 at an MTV performance.