He received his Bachelor of Arts, summa cum laude, from Harvard College in 1976, graduating Phi Beta Kappa.

[5] From 1981 to 1983, he was Special Assistant to Judge William H. Webster, Director of the Federal Bureau of Investigation.

[6] In 1983, he was appointed Assistant United States Attorney for the District of Massachusetts, serving as Chief of Public Corruption Division from 1988 to 1991.

He was also an outspoken opponent of mandatory minimum sentences, having told the Judiciary Committee in 2015, "If you do not abolish minimum mandatory sentences for drug offenses, you must accept the tragic fact that this disparate treatment of persons of color will be allowed to continue.

[11] In April 2020, Grants wrote a concurrence arguing against a bright line rule defining where use of automatic number-plate recognition cameras becomes an unconstitutional search when the unanimous court upheld their warrantless use on bridges to Cape Cod.