The supreme court of the US state of Minnesota has ruled that a vacant senate seat should be granted to Al Franken, a Democrat, more than seven months after the US elections.

Franken, who is also a popular comedian and author, was granted the seat over Norm Coleman, the Republican incumbent, by the court on Tuesday.

"Al Franken received the highest number of votes legally cast and is entitled under Minnesota statute... to receive the certificate of election as United States senator from the State of Minnesota," the court ruling said.

Tim Pawlenty, the Minnesota governor and a Republican, is now expected to formally grant the senate seat to Franken.

Legal battle

Franken had been engaged in a months-long legal fight over the validity of the November 4 election.

A series of recounts in the state gave him a victory of just 312 votes over Coleman, prompting the Republican to challenge the accuracy of the recount.

Coleman has the option to appeal the decision to the US supreme court.

Should Franken be seated, Democrats would possess the 60 senate votes needed to prevent opponents from forcing a filibuster, a tactic which delays the passage of legislation through parliament through the method of protracted debate.

Further control of the senate would give Barack Obama, the US president, increased power to advance his legislative agenda.

The Democrats already have a strong majority in the House of Representatives, the lower house of the US’ bicameral legislature.