[3] His ability to do things without specific instructions and his familiarity with public officials and affairs attracted Roosevelt's notice and Loeb became his private secretary in 1899.

On September 14, 1901, on the night President William McKinley died after being shot by an assassin eight days earlier, Loeb met Vice President Roosevelt during his dash to Buffalo at the North Creek, New York train station delivering the telegram from Secretary of State John Hay announcing McKinley's death at 2:15 that morning.

In addition, in his own autobiography, Roosevelt stated that Loeb was responsible for starting the investigations into the frauds committed by the Sugar Trust in New York's Custom House.

Roosevelt accepted Root's decision and told Loeb that his choice then was William Howard Taft, saying that he had the experience to run the government.

[11] He later went on to become Vice President of the American Smelting and Refining Company and retired to a quiet life in Oyster Bay where he lived with his wife and son, William Loeb III.

William Loeb Jr. died on 19 September 1937 in Glen Cove, Nassau County, New York, at age 70.