In 1818 and 1819, he leased the rights to the mill and seigneury at L'Isle-Verte; in 1849, he purchased the title to the seigneury.
He built a sawmill and then another one in partnership with others.
He also owned a wharf and boats at L'Isle-Verte.
Bertrand was captain in the local militia, becoming lieutenant-colonel in 1862.
He served as commissioner for the small claims tribunal.
He was elected to represent Rimouski in the Legislative Assembly of Lower Canada in an 1832 by-election; he was reelected in 1834.
Bertrand supported the Ninety-Two Resolutions.
In 1844, he was elected to the Legislative Assembly of the Province of Canada for Rimouski.
In 1845, he became the first mayor of L'Isle-Verte.
Bertrand died at L'Isle-Verte in 1871.
His son Charles was a member of the Canadian House of Commons.
His home at L'Isle-Verte, the Maison Louis-Bertrand, has been designated a National Historic Site of Canada.