Tweedie became the tenth premier of New Brunswick in 1900 and led the party to a large majority government in the 1903 election.

Tweedie's government allowed women to be admitted to the practice of law in 1906 and supported the development of hydroelectric power at Grand Falls.

He also created a Workers' Compensation board and successfully lobbied the federal government to increase subsidies to the province including payment for railway expansion.

A supporter of educational institutions, Tweedie personally donated academic prizes for students.

Lemuel Tweedie died in 1917 at age sixty-seven in his home town of Chatham[1] and was buried in the Riverside Cemetery.