Cornelius was born to Ulrich and Gisela Sommer in Germany on July 21, 1948. In 1954, Cornelius immigrated to Canada with his parents and his sister, Angelika. Cornelius and his family settled in Georgetown, Ontario. After graduating high school, Cornelius completed a Bachelor of Arts in Toronto, Ontario.

During the 1970s, Cornelius worked and had various jobs in factories, workshops and on farms in an effort to save money so he could travel. Subsequently, he spent approximately one year travelling around Western Europe.

When Cornelius returned from his travels, he obtained a Bachelor of Laws (LL.B) and eventually opened his own law firm in Toronto, Ontario.