The 1968 Warsaw Pact invasion of Czechoslovakia interrupted Čížek's doctoral studies, which he was pursuing while working as a Junior Scientist at the Institute of Physical Chemistry in Prague, and forced him to leave his native country. He moved to Canada to join the Department of Applied Mathematics at the University of Waterloo as an associate professor. Later, he was cross-appointed to the Department of Chemistry in 1973 and was promoted to full professor in 1975. He also served two terms on the University of Waterloo's Senate, the first one from 1977–80 and the second from 1985–88, and held positions as affiliate professor at University of Florida in Gainesville (appointed in 1982) and Adjunct Professor at Charles University (appointed in 1995). Following the 1989 Velvet Revolution, in 1991 he was able to present and defend his doctoral thesis at the Czechoslovak Academy of Sciences. He retired from the University of Waterloo in 1996 and received the title of Distinguished Professor Emeritus, and is also a permanent Visiting Professor at Charles University.
