He won the 1913 Nobel Prize in Physics for (in the words of the committee) "his investigations on the properties of matter at low temperatures which led, inter alia, to the production of liquid helium".
In 1908 Onnes was the first physicist who made this liquefaction of helium possible. For this purpose he founded a cryogenics lab, in 1904. Here he managed, using the Joule-Thompson effect, to lower the temperature to less than one degree above the absolute minimum (0,9°K). By then this was by far the coldest place on earth.
He was born in Groningen, Netherlands and studied under studied under Robert Bunsen and Gustav Kirchhoff at the University of Heidelberg. From 1882 to 1923 he served as professor of experimental physics at the University of Leiden.
He died in Leiden.
The instruments Onnes devised for his experiments can still be seen at the Boerhave museum in Leiden. see below