The couple announced in June that they have got engaged after three years of dating on-and offwith Cyrus saying that she "looks forward to a life of happiness with Liam".
Luke - who played Nathan Tyson on soap opera Neighbours - has now offered his blessing to the pair and praised Cyrus as a wonderful addition to his family.
"She's great. She loves our kids, and our kids absolutely love her. She won our hearts," Luke told Entertainment Weekly.
He continued: "I find her really interesting. I find her very articulate, and years in maturity above her age. But at the same time, she's very much like Liam.
"I think a lot of people don't realise that they are really, really in love. They actually are a perfect match in a lot of ways."
Luke is married and has two children with his wife Samantha.
Liam mistakenly suggested that he and Cyrus were already married at the Australians in Film Awards 2012 gala last week.