He was married to his seventh cousin Claudine Grimaldi in 1465, per the wishes and legal Will and testament of her late brother,[1] Catalan, and their father.
[2] Grimaldi found much help and support as a ruler from his brothers[2] and, following his feud with the faction headed by Claudine's mother, Pomellina Fregoso, Lambert secured his title and an "oath of fidelity"[1] from the population of Monaco.
Claudine was nominally her brother's successor, but all power as Seigneur of Monaco was in her husband's hands and their marriage legitimized the succession for their descendants.
[2] Lamberto assumed the reins of power in Monaco at a difficult time in its often vulnerable history.
Lamberto fought to preserve Monaco's independence, and is said to have "handled diplomacy and the sword with equal talent".