My husband was born in France to a french mother in 1959. She put him up for adoption at age 5 and he was adopted by US parents. He went to US aged 9 and they applied for him to become a US citizen.
Does anyone know if he can now claim french citizenship? I am british and his wife. He wants to come here to join me but the UK won't allow it because he has a criminal conviction. If he can claim dual nationality because he was born in France, then he can come to the UK and live and work here.
If anyone can direct me to a legitimate site or answer (preferably in english) that's be great!

Whether or not he gets French citizenship all countries reserve the right to refuse applicants (from any country) based on criminal history.

Im sure he could apply for citizenship easily enough, he just has to file and claim he was removed from the country as a child and wishes to return, they should help him out. Contact the nearest consulate in the US