Became an associate judge in 1986 and served until 1995, when he was not retained in a secret vote by circuit judges
As an associate judge in 1990, Stack challenged and lost to then-temporarily appointed Circuit Judge Nicholas Byron in a Democratic primary for a full term.
Appointed to the 3rd Circuit Court in February 2003 to succeed retired judge P. J. O'Neill.
Served eight years as a special assistant Illinois attorney general and one year as an assistant U.S. Attorney based in East St. Louis
In 1978, Stack ran as a Republican for U.S. Congress versus longtime incumbent U.S. Rep. Mel Price (D-East St. Louis). "The only time I voted Republican in a primary election was when I ran then," he told the St. Louis Post-Dispatch. "I've always considered myself an old-line Democrat."