Martin, who was staying with the father and daughter during August 2009, said the experience had reminded him of an attempted sexual assault he had suffered when he was eight or nine years old.
The court in the central Limousin region handed down a sentence that was less than the 20 years called for by the public prosecutor.
"I'm sorry for what I did... I'm so sorry... I hope that thanks to prison I can become a man again and think of the direction I now want to give to my life," Martin told the court through an interpreter.
His ex-girlfriend, Hannah Bradshaw, told the court that her father had admitted having a sexual relation with Martin.
Martin's lawyer Lionel Magne told the court that "five psychiatrists who treated him... all said he was schizophrenic" and therefore not responsible for his acts. He has been hospitalised several times since being arrested and charged and in September 2009 tried to commit suicide.
Public prosecutor Henri-Michel Perret said "this is a killing that was carried out in a cowardly way, with incredible sang-froid. Here we have someone who killed, certainly not a benefactor, but all the same a man who offered him hospitality."
The court heard that Martin, the son of a craftsman and a teacher, had a troubled childhood before spending three years in the British army. He served in Iraq before he was kicked out for taking cannabis.