The 47th Maine Legislature soon passed a bill to charter the Belfast and Moosehead Lake Railroad Company, which was signed by Governor Joshua L. Chamberlain on February 28, 1867.

On April 6, 1867, and March 28, 1868, the people of Belfast voted by margins of 865-27 and 854–50, respectively, to authorize the city to issue 30-year, 6-percent bonds to finance their purchase of B&MLRR stock.

This would eventually represent 83% of the company's outstanding shares, the rest of which were purchased by several other towns along the line (Brooks, Unity, and Thorndike), and by about 100 private investors, mostly from Belfast and Boston.

Ground was broken on the Belfast waterfront on August 4, 1868, at what would become the site of the road's terminal and main yard (milepost "0") for the next 138 years.

The railroad's "Last Spike" was driven near Brooks on September 24, 1870, completing a line that stretched 33.07 miles from Belfast inland to Burnham Junction.

Most freight during this period was southbound, consisting largely of grain for poultry production in the area, as well as smaller amounts of fish oil, leather, coal, lumber and fertilizer.

With the decline in American railroad profitability in the 20th century, the Maine Central discontinued its lease of the Belfast Branch on January 1, 1926.

It operated diesel excursion runs from Belfast to Waldo and diesel-and steam-powered trains from Unity to Burnham Junction.

The year also saw the railroad purchase a steam locomotive, SJ B number 1149,[4] from the Swedish State Railways for its Unity excursions.