Unzaga accompanied Alejandro O'Reilly to New Orleans in 1769 to put down the Rebellion of 1768 by French and German colonists objecting to the cession of Louisiana to Spain via the Treaty of Fontainebleau (1762).

[3] Luis de Unzaga was one of the driving forces behind the birth of the United States, for which he made use of a robust secret network of family contacts.

During the summer of 1776, he secretly helped Patrick Henry and the Americans by privately delivering five tons of gunpowder from the king's stores to Captain George Gibson and Lieutenant Linn of the Virginia Council of Defense.

After repeated requests from New Orleans merchant Oliver Pollock, Unzaga approved the secret transfer of a load of gunpowder up the Mississippi and Ohio rivers to Fort Pitt, where it arrived in May 1777.

Later he continued to attend to the requests for help from George Washington and Robert Morris to finally achieve the birth of the United States of America.