Liberal Leader Brian Gallant is running for his party, while Jimmy Bourque is the Progressive Conservative candidate and Susan Levi-Peters is running for the New Democrats.
More than 1,400 of the 8,800 eligible voters cast their votes in advance.
Shale gas exploration and the impact of changes to the federal Employment Insurance program emerged as the main issues during the four-week campaign.
The byelection was called when former Liberal premier Shawn Graham quit politics after he was found to be in a conflict of interest over a $50-million loan guarantee his government gave to a construction firm in 2009.
The province's conflict of interest commissioner said Graham should have removed himself from cabinet discussions about the loan guarantee to Atcon because it had ties to his father.
Entering the byelection the Progressive Conservatives had 41 seats in the legislature, the Liberals have 12, while there is one independent and one vacancy.