The baby was born as the 26-year-old actress left court after the latest hearing into allegations she lied to police officers investigating a traffic accident she was involved in last year, reported TMZ online.
Michael and his bride-to-be have named their firstborn Landon Major Lohan.
Michael was by his fiancee's side throughout the delivery.
Besides Lindsay, Michael has a daughter, Ali, and two sons, Cody and Michael Jr, from his marriage to ex-wife Dina. He also fathered a lovechild with a former mistress, Kristi Horn.
A televised DNA test last year proved he was the biological father of her daughter Ashley, 17.