With over two-thirds of the vote counted in Maine on Sunday, Sanders secured 63.8 percent of the voters' support, while his main rival, Hillary Clinton, gained 36 percent of the votes.
In total, Sanders is currently in second place behind Clinton, having won in eight of the 19 states in which Democrats have voted to select their presidential candidate.
During 'Super Saturday', Sanders won the Kansas and Nebraska primary votes, while Clinton won in Louisiana.
Clinton and Sanders are vying to secure at least 2,383 of the 4,764 delegates to the Democratic Party Convention in July, where the party will select its presidential candidate. Clinton has already gained the support of 1,121 delegates, compared to Sanders' 481. However, many are upset that the party doesn't allocate all of its delegates according to the results of the state primary elections; so-called 'superdelegates' exist who may pick which candidates they like, and the overwhelming majority back Hillary Clinton, who is considered an 'establishment' candidate.