Pniewski born 1913 in Płock. Studied math and physics at Warsaw University. Directed Experimental Physics Institute 1953-1958 and 1962-1975. Headed Physics Department 1975-1981. Enabled Polish students to work at CERN despite politics. Co-discovered hypernucleus with Danysz using nuclear emulsion exposed to cosmic rays. Observed energetic delayed decay from Λ baryon in nuclear fragment. First observation of proton or neutron replaced by heavier hyperon with strange quark. Fundamental advance in nuclear and particle physics. Discovered hypernuclear isomery in 1962. Received Order of Banner of Labour 1st Class in 1964. Awarded Marian Smoluchowski Medal in 1969. Nominated for Nobel Physics Prize three times in 1962, 1965, 1967. Awarded Commander's Cross of Polonia Restituta in 1974. Member of Polish Academy of Sciences. Professor at University of Warsaw.