Mullett Lake is a lake in the northern tip of lower Michigan. The lake is named after John Mullett, who, together with William A. Burt, made a federal survey of the area from 1840 to 1843. A neighboring lake was named after Burt.

The lake is approximately 10 miles (16 km) long from southeast to northeast, about 4 miles (6.4 km) at its widest, and 120 feet (37 m) at its deepest. It covers 17,360 acres, making it the third largest inland lake in Michigan.

Major inflows to the lake are the Indian River, which connects with nearby Burt Lake, Pigeon River, Little Pigeon River, and Mullett Creek. The Cheboygan River flows out of the northeast end of the lake.

The lake is part of the great Inland Waterway, by which one can boat 38 miles (61 km) from Crooked Lake and Round Lake near the Little Traverse Bay of Lake Michigan across the northern tip of the lower peninsula's so-called mitten to Cheboygan on Lake Huron.

The Inland Waterway was a Native American trade route that was later opened to small steamer and modern recreational traffic.

I-75 passes to the west of the lake, with two interchanges near the south end of the lake at the unincorporated community of Indian River. M-27 passes along the northern shore of the lake through the unincorporated communities of Mullett Lake and Topinabee, while M-33 running north-south passes along a portion of the eastern shore through the community of Aloha.

Mullett Lake is an excellent fishery, with a variety of game species, including brown trout, brook trout, rainbow trout, steelhead, splake, smelt, northern Pike, muskellunge, yellow perch, walleye, smallmouth bass, largemouth bass. Most notably lake sturgeon (the state record specimen was taken from these waters) are making a comeback.

Mullet Lake has a historical, former Michigan Central passenger train ticket station. The station sits directly at the end of Polish Line Road and has about 200 feet of lake front property. It was bought (1950) by an old Michigan Central railroad employee once it shut down and was turned into a family cottage which is still used today (2008). The "Old Depot" which is the nickname for the cottage was the main connection between Detroit and Mackinaw.