M-77 is a state trunkline highway in the Upper Peninsula (UP) of the US state of Michigan. It runs from US Highway 2 (US 2) near Blaney Park in the south to Grand Marais in the north. The highway borders the Seney National Wildlife Refuge. The northern half has been designated as a Scenic Spur of the Lake Superior Circle Tour. Originally designated by 1919, the highway has not been changed much in its history. By the late 1950s, the highway was paved, completing the modern M-77 highway.

From US 2 near Blaney Park going north, M-77 runs past the former Blaney Park Resort and out of town by a small private airport next to Lake Ann Louise. The highway continues through rural woodlands past Chip Lake. The road crosses the Manistique River as it runs through Germfask. From just south of Germfask to just south of Seney, the road forms the eastern boundary of the Seney National Wildlife Refuge.

The refuge is a managed wetland in Schoolcraft County in Michigan. Established in 1935, it has an area of 95,212 acres (38,531 ha) bordered by M-28 and M-77 that is the remains of the Great Manistique Swamp, a perched sand wetland located in the central UP. The refuge contains the Strangmoor Bog National Natural Landmark within its boundaries. During the 1930s, work crews employed by the Civilian Conservation Corps (CCC) rebuilt, restored, and expanded the wetland drains, this time for active wetlands management purposes. These CCC ponds and drains are still used by the wetlands managers that staff the current National Wildlife Refuge.

At Seney, M-77 crosses a line of the Canadian National Railway and turns east along M-28. Both run concurrently for less than half a mile (0.8 km) over a crossing of the Fox River before M-77 turns back northward. About 11 miles (18 km) north of Seney, the road turns sharply to the west, near Snyder Lake. The trunkline continues along several other lakes before turning northeasterly and then northward. The road marks the westernmost extent of the Pictured Rocks National Lakeshore around 2.5 miles (4.0 km) south of Grand Marais. M-77 intersects H-58 in town and ends north of there by the Grand Marais harbor.

Grand Marais is situated on the shores of Lake Superior some 25 miles (40 km) north of the mainline of the Lake Superior Circle Tour. Since the Tour runs only along state trunklines in Michigan, a Scenic Spur of the tour was created to route traffic north from Seney to Grand Marais. The scenic spur also terminates in Grand Marais with M-77 north of the junction with H-58.

M-77 is maintained by the Michigan Department of Transportation (MDOT) like other state highways in Michigan. As a part of these maintenance responsibilities, the department tracks the volume of traffic that uses the roadways under its jurisdiction. These volumes are expressed using a metric called annual average daily traffic, which is a statistical calculation of the average daily number of vehicles on a segment of roadway. MDOT's surveys in 2009 showed that the highest traffic levels along M-77 were the 1,924 vehicles daily between Floodwood and Ten Curves roads in Schoolcraft county; the lowest counts were the 799 vehicles per day north of M-28 in Seney. No section of M-77 has been listed on the National Highway System, a network of roads important to the country's economy, defense, and mobility.

The route was first designated by July 1, 1919, with a route very close to its present course. A pair of sharp turns were straightened 11 miles (18 km) north of Seney at Lavender Corner around 1950. The last segments of gravel road were paved in 1958–59.