The name Keith comes from a warrior whom Malcolm II dubbed "Marbhachair Chamuis" or Camus Slayer after the warrior slew the Danish General Camus at the Battle of Barrie in 1010. "Marbhachair Chamuis" later held the lands of Keth in Lothian for Malcolm II. This is the origin of the modern name Keith.

A Norman named Hervey later married the heiress of Marbhachair and received charter for the lands of Keth from King David I in 1150. Hervey's son was made Marischal of the King of Scots in 1176. The Marischal, was custodian of the Royal regalia and was to protect the King at Parliament

Robert the Bruce bestowed Halforest in Aberdeenshire to Robert de Keth in 1308. Here the Keiths built their castle. Sir Robert's nephew was the one to return the Bruce's heart to Melrose abbey after the Douglas's death at the hands of the Moors in Spain. The Bruce also made the office of Marischall herediatry to the Keiths in 1324 in recognition of Sir Robert de Keth, calvalry commander at the Battle of Bannockburn.

Sir William the Marischall added estates in Buchan, Kincardine and Lothian to the family by marrying the daughter of Sir Alexander Fraser, the High Chamberlain. Sir William's brother married the Cheyne heiress bringing the massive estate of Inverugie into the familly. The chief's seat was later to be a castle on the Inverugie lands.

The 3rd Lord Keith was raised to Earl Marischal in 1458. During the reformation the 7th Earl was captured and imprisoned in the Tower of London until the restoration. The King then appointed him Privy Councillor and later Lord Privy Seal as reward for his services in the Royal cause. The Earl Marischal had hidden the Honours of Scotland (Scottish crown jewels) on Keith lands for safekeeping