Odo I was the eldest son and heir of Josselin I of Porhoët.
During the reign of Conan’s brother-in-law and heir Hoël of Cornouailles, he even joined several lords who had rebelled against the duke in 1068.
He married firstly Anne, or Emma, de Léon, who died in 1092.
She was the aunt of Guihomar II, Viscount of Léon.
They had five children: After Emma’s death, Odo married again.