He worked in private practice in The Hague before moving to New York City on a Fulbright scholarship,[3] where he earned a master's degree at Columbia in 1953 and graduated first in his class with an LL.B.
[4] Smit worked for Sullivan & Cromwell for two years before joining the Columbia Law School faculty in 1960 as director of the Project on International Procedure.
[3][5] He was credited for helping to revise section 1782 of Title 28 of the United States Code.
In 1978, Smit was appointed to the Stanley H. Fuld Chair at Columbia Law School.
[3] Smit was a water polo player who played for New York Athletic Club.