[5] In December 1849, Steele was appointed Chargé d'Affaires to Venezuela by U.S. President Zachary Taylor, a member of the Whig Party from Kentucky, during a recess of the U.S. Senate.

While in his post, he had to contend with Venezuela radical Narciso López, who led repeated filibustering expeditions in an attempt to conquer the island of Cuba, then a colony of Spain.

[8] López made several generous offers to American military leaders to support him, but Taylor and his Secretary of State, John M. Clayton, viewed the enterprise as illegal, issuing a blockade, and later,[9] authorized the arrest of López and his associates for breach of the Neutrality Act, although they were eventually acquitted by friendly Southern juries.

Fillmore and his Secretary of State, Daniel Webster, worked out a series of face-saving measures with the Spanish that settled the crisis without armed conflict.

[10] Reportedly, Steele narrowly escaped death when a band of robbers broke into the United States legation at Caracas in an attempt to steal the money of diplomatic representatives held for safe-keeping by the chargé d'Affaires.

Steele was noted for "the clearness of his statements, the strength and force of his logic and his power as a cross-examiner" and appeared before the Supreme Court of the United States.

[1] Together, Isaac and Rosa were the parents of five sons and three daughters, including:[5] Steele died at his home, 14 West Madison Street in Mount Vernon, Baltimore, on April 11, 1891, just shy of his 82nd birthday.

His countenance, his manner, his walk and conversation bespoke not only the student learned in all the principles and abstruse points of his profession, but also showed the man who loved it, and believing in it honored it at all times and under all circumstances.