Thompson Falls sits on US Highway 2, which runs east-west across northern Montana and is the main travel corridor between Spokane, Washington and Glacier country. It is roughly 90 miles east of Libby, 60 miles west of Plains, and about 100 miles northwest of Missoula via State Highway 200 (the more direct route if coming from the east). There is no commercial air service, train service, or intercity bus to Thompson Falls itself.
By car is the practical approach. From Missoula, take I-90 west to St. Regis and then follow State Highway 135 north to Thompson Falls — about 90 minutes. From Spokane, US-2 east across the Idaho panhandle is the direct route, taking just under two hours. From Glacier National Park, US-2 west from Browning and Kalispell is the most direct, running about 2.5 to 3 hours depending on your starting point within the park.
There is no public transit to or within Thompson Falls. Gas stations are present in town and reliable on US-2 through the corridor, though the mountain passes into Idaho can be isolated in winter — keep your tank reasonably full if you are traveling in November through March. Cell service in the Clark Fork valley is patchy in places; download offline maps before you leave the highway if you plan to venture into the Cabinet Mountains.