He was born in Hanau, Germany and in 1803 he started studying law at the University of Marburg, one year after his brother Jacob started there. The whole of the lives of the two brothers were passed together. In their school days, they had one bed and one table in common. As students, they had two beds and two tables in the same room. They always lived under one roof, and had their books and property in common.

In 1825 Wilhelm married a pharmacist's daughter; Henriette Dorothea Wild, also known as Dortchen, at age 39. Wilhelm's marriage in no way disturbed the harmony of the brothers. As Richard Cleasby said, “they both live in the same house, and in such harmony and community that one might almost imagine the children were common property.”Together, Wilhelm and Henriette had four children: Jacob Grimm (3 April 1826–15 December 1826), Herman Friedrich Grimm (6 January 1828–16 June 1901), Rudolf Georg Grimm (31 March 1830–13 November 1889), and Auguste Luise Pauline Marie (21 August 1832–9 February 1919).

Wilhelm's character was a complete contrast to that of his brother. As a boy he was strong and healthy, but as he grew up he was attacked by a long and severe illness, which left him weak all his life. His was a less comprehensive and energetic mind than that of his brother, and he had less of the spirit of investigation, preferring to confine himself to some limited and definitely bounded field of work; he utilized everything that bore directly on his own studies, and ignored the rest. These studies were almost always of a literary nature.

Wilhelm took great delight in music, for which his brother had but a moderate liking, and had a remarkable gift of story-telling. Cleasby, in the account of his visit to the brothers quoted above, relates that “Wilhelm read a sort of farce written in the Frankfort dialect, depicting the ‘malheurs’ of a rich Frankfort tradesman on a holiday jaunt on Sunday. It was very droll, and he read it admirably.” Cleasby describes him as “an uncommonly animated, jovial fellow.” He was, accordingly, much sought in society, which he frequented much more than his brother.

From 1837-1841, the Grimm Brothers joined five of their colleague professors at the University of Göttingen to form a group known as the Göttinger Sieben (The Göttingen Seven). They protested against Ernst August, King of Hanover, whom they accused of violating the constitution. All seven were fired by the king.

Wilhelm Grimm died in Berlin of an infection at the age of 73.

In Terry Gilliam's The Brothers Grimm, Academy Award winner Matt Damon played a fictionalized version of Wilhelm. A slightly less fictionalized version of Wilhelm was played by Laurence Harvey in the 1962 film The Wonderful World of the Brothers Grimm.

a. The Neue Deutsche Biographie records their names as"Grimm, Jacob Ludwig Carl" and "Grimm, Wilhelm Carl". The Deutsches biographisches Archiv records Wilhelm's name as "Grimm, Wilhelm Karl". The Allgemeine deutsche Biographie gives the names as "Grimm: Jacob (Ludwig Karl)" and "Grimm: Wilhelm (Karl)". The National Union Catalog Pre-1956 Imprints also gives Wilhelm's name as "Grimm, Wilhelm Karl".