Zorich, 44, addressed a federal judge in Chicago, saying he chose not to file his taxes "in a timely fashion."
- DOWNLOAD: Read the complaint against Zorich (pdf)
"And you knew it was wrong to do that?" asked U.S. Magistrate Judge Daniel Martin.
"Yes, your honor," Zorich said.
The magistrate then asked Zorich's plea to all four counts.
"Guilty, your honor," Zorich said.
During that time, Zorich allegedly made more than $1 million, including income from a charity he founded.
Zorich is free on bond and has been cooperating with the IRS. He faces a maximum penalty of one year in prison.
The Chicago native was on the 1988 Notre Dame team that won a national championship. He played for the Bears from 1991 to 1996, and ended his career with the Washington Redskins in 1997.
Zorich must pay $71,000 in back taxes as part of a plea agreement. He is to be sentenced July 12.
The Associated Press contributed to this report.