Robert Watson Grimmer (October 25, 1866 – November 4, 1948) was a merchant and politician from New Brunswick, Canada.
He was born in Saint Stephen, New Brunswick, the son of William Wey Grimmer and Margaret Wilson.
Grimmer served on the town council for Saint Stephen and was mayor from 1908 to 1909.
He also served on the St. Stephen Water Commission and as a school trustee.
Grimmer was a Mason and a member of the Knights of Pythias.