Nicholas III, Lord of Mecklenburg (after 1230 – 8 June 1289 or 1290) was from 1264 to 1289 Lord of Mecklenburg.
He was the son of John I and his wife, Luitgard of Henneberg (1210-1267), the daughter of Count Poppo VII of Henneberg. On 9 January 1266, he was appointed canon of Lübeck Cathedral. In 1269 he was also a priest in the St. Mary's Church in Wismar.
When Henry I was taken prisoner during a pilgrimage to the Holy Land, Nicholas III and his brother John II took up the regency for Henry's underage sons. He is last mentioned as living in a document dated 2 April 1289.
He died on 8 June 1289 or 1290 and was buried in Doberan Minster.