In 33 games with the Golden Bears, Sebastian amassed 96 tackles, three passes defended and two interceptions.
In 2013, he played in only one game before tearing his Achilles and missing the rest of the season.
Sebastian recorded only 21 tackles over seven games last season while hampered by a quad injury.
"I'm very thankful to head coach Brian Kelly and the rest of the coaching staff and administration for giving me the opportunity to come play at the University of Notre Dame," said Sebastian, who graduated from Cal in December. "I think academically, spiritually and athletically will make Notre Dame a perfect fit. I've got one year to make an impact and I plan on making the most of this opportunity. I look forward to joining the Notre Dame family.
"I'm eager to meet my teammates. Like the coaching staff and players alike, our objective is to field a better product than the year before. My hope is that we field one of college football's best teams this upcoming year. I've got veteran experience in the secondary, and familiarity with multiple defenses and opposing offenses."
Notre Dame ranked 84th nationally in passing yards allowed per attempt last season. The Irish finished 8-5.
- Chris Johnson