Castle Campbell was originally called Castle Glume (Gloom) when it was built in the late 15th Century. It was first owned by Walter Stewart of Lorne. It became Colin Campbell's keep, the first Earl of Argyll, when he married Elizabeth Stewart in 1465, an heiress of the estate. At his request, the name of the castle was changed to Campbell Castle by King James IV in an act of Parliament in 1489. The castle remained in the hands of Clan Campbell for several generations and hosted Mary Queen of Scots in 1563. The castle was occupied by Cromwell's forces in 1653 and partially burnt by General Monck in 1654. The castle was owned by the Taits and Orrs in the 19th and 20th centuries, until the National Trust for Scotland took it over in 1948.
The buildings within the castle include a tower house, hall, chamber range, and an east range. The tower house has four main floors. The ground floor contains a vaulted storage cellar. An upper entrance, once reached by an outside staircase, leads into the hall, the principal reception room. An original narrow spiral staircase was replaced in 1600 by a more substantial one. The terrance gardens are located to the south.
The second and third floors of the tower were most likely used as private chambers. It is possible that the hall and chamber range served as the residence for the Earls of Argyll, since the reception room and the east end were on a much grander scale. This part of the castle now lies in ruins.
The east range dates from about 1600 when it was remodeled. The south-west corner of the rocky knoll is locally referred to as John Knox's Pulpit. To the west of the castle there would have been a kitchen garden.