Davezac completed his education in France and moved to the United States shortly after Louise's marriage, studying medicine in Edenton, North Carolina, and establishing a practice in Accomack County, Virginia.

In 1814 he joined the staff of Andrew Jackson as aide-de-camp and judge advocate with the rank of Major, the title by which he was addressed for the rest of his life.

[6] In 1829 Jackson rewarded Davezac with appointment as Secretary of the United States embassy in the Netherlands, where he served under William Pitt Preble.

[8] Davezac returned to New Orleans, but soon relocated to New York City, where he was active in Martin Van Buren's unsuccessful 1840 campaign for reelection.

[9][10] In 1844 Davezac supported Van Buren's efforts to win the Democratic nomination for President, and campaigned extensively for the eventual nominee, James K. Polk.