The 14-kilometre (8.7 mi) long fjord is located along the Skaggerak coast in the traditional district of Grenland and it forms the border with the municipalities of Bamble, Skien, and Porsgrunn.

The fjord stretches from the opening to Langesundsfjord in the south to the mouth of the Porsgrunn River in the north.

The much smaller fjord of Gunneklevfjord opens into the Porsgrunn/Skien River and is separated from Frierfjorden by the peninsula of Herøya.

[1] The Frierfjorden narrows to a width of about 300 metres (980 ft) at Breviksstrømmen, the mouth of the fjord, where the town of Brevik sits on the northern side and the town of Stathelle lies on the southern side.

The name is derived from the word fríðr which means "beautiful" or "lovely".