Being a pioneer lawyer was a physically challenging profession, often requiring long travel by horseback through wilderness over Indian trails in all types of weather to attend the territorial courts in Cincinnati, Marietta, or Chillicothe, Ohio.

[3] In December of 1811, following the Battle of Tippecanoe, Sibley chaired a public meeting which drafted a memorial to the President and Congress, concerning the defenses of Michigan Territory.

[5] During the war, Sibley commanded a company of riflemen in defense of Detroit, though the British attack was successful and William Hull surrendered the fort.

Sibley was appointed as the first United States Attorney for the Michigan Territory by U.S. President James Madison, serving from 1815 to 1823.

[3] When William Woodbridge resigned on August 9, 1820, as territorial Delegate to the 16th United States Congress, Sibley was elected to fill the vacancy.

During this period, Sibley was also commissioned, along with Lewis Cass, to negotiate the August 29, 1821, Treaty of Chicago with the Ottawa, Potawatomi, and Chippewa, in which the tribes ceded most of their territory south of the Grand River.

A daughter, Catherine Whipple Sibley, married Charles Christopher Trowbridge, mayor of Detroit in 1834 and unsuccessful candidate for Governor of Michigan in 1837.