In 1901, Garrett embarked on a diplomatic career with appointment as Secretary of the United States legation at The Hague.
 In 1905, he transferred to a similar position in Berlin, and in 1908 another transfer brought him to Rome.

Garrett was appointed Minister to Venezuela in 1910 and served until 1911, when he was appointed as Minister to Argentina.

In 1914, Garrett left Argentina when he was appointed as a special assistant to the Ambassador to France.
 He served in this post until 1917.
 As an American diplomat in Europe during World War I, Garrett took part in commissions and conferences on the handling of prisoners of war and other war-related issues.

From 1917 to 1919, Garrett served as Minister to the Netherlands and Luxembourg.

Originally a Democrat, Garrett later became a Republican and served as a Delegate to the 1920 Republican National Convention.
 In 1922 he was an unsuccessful candidate for the Republican nomination for U.S. Senator, losing to incumbent Joseph I. France.
 (France went on to lose the general election to William Cabell Bruce).
 In 1924, he was again a Delegate to the Republican National Convention.

Garrett served as Ambassador to Italy from 1929 to 1933.
In 1901, Garrett embarked on a diplomatic career with appointment as Secretary of the United States legation at The Hague.  In 1905, he transferred to a similar position in Berlin, and in 1908 another transfer brought him to Rome.
Garrett was appointed Minister to Venezuela in 1910 and served until 1911, when he was appointed as Minister to Argentina.
In 1914, Garrett left Argentina when he was appointed as a special assistant to the Ambassador to France.  He served in this post until 1917.  As an American diplomat in Europe during World War I, Garrett took part in commissions and conferences on the handling of prisoners of war and other war-related issues.
From 1917 to 1919, Garrett served as Minister to the Netherlands and Luxembourg.
Originally a Democrat, Garrett later became a Republican and served as a Delegate to the 1920 Republican National Convention.  In 1922 he was an unsuccessful candidate for the Republican nomination for U.S. Senator, losing to incumbent Joseph I. France.  (France went on to lose the general election to William Cabell Bruce).  In 1924, he was again a Delegate to the Republican National Convention.
Garrett served as Ambassador to Italy from 1929 to 1933.
John W. Garrett (diplomat)