SR 139 begins at an intersection with
U.S. Route 201A,
U.S. Route 2, and
SR 8 in
Norridgewock. The intersection of SR 139 and U.S. Route 2 is notorious for being one of the most dangerous intersections in central Maine. SR 139 then heads south and joins
SR 104 for a 2.78 mile
concurrency, during which it intersects with
SR 23, followed by an
interchange with
Interstate 95. The section of SR 139 between U.S. Route 2 in Norridgewock and Interstate 95 in Fairfield is often used as a bypass of U.S Route 2 through Skowhegan. From the interchange with Interstate 95, as it heads east there is a 0.22 concurrency with
U.S. Route 201 in
Fairfield and then a 2.23 mile concurrency with
SR 11 and
SR 100 in
Benton. SR 139 continues on to have a 0.18 mile concurrency with
U.S. Route 202 and
SR 9 before once more being without concurrent routes for 0.69 miles in
Unity and then begins a 3.5 mile concurrency with
SR 220 in
Thorndike. SR 139 intersects Former
SR 203 at its then northern terminus and then
SR 7 as it continues through
Brooks. It then continues into
Monroe, where it intersects
SR 141 at SR 141's northern terminus. From there, SR 139 has a 1.67 mile concurrency with
SR 69 and reaches its western terminus at US Route 1A in
Winterport. ==Major junctions==