"So help me God" is a phrase often used to give an oath, sometimes optionally as part of an oath of office. It is used in some jurisdictions as an oath for performing a public duty, such as an appearance in court. The phrase implies greater care than usual in the truthfulness of one's testimony or in the performance of one's duty.
Australia
In Australia the Oath of Allegiance is available in two forms, one of which contains the phrase "So help me God!"
Canada
In Canada, the Oath of Office, Oath of Allegiance, and Oath of Members of the Privy Council may be sworn, and end in "So help me God." They may also be solemnly affirmed, and in such case the phrase is omitted.
Fiji
The Constitution of Fiji, Chapter 17 requires this phrase for the oath of allegiance, and before service to the republic from the President's office or Vice-President's office, a ministerial position, or a judicial position.
New Zealand
In New Zealand the Oath of Allegiance is available in English or Māori in two forms, one an oath containing the phrase 'so help me God' and the other an affirmation which does not. The Police Act 1958 and the Oaths Modernisation Bill still includes the phrase.
United Kingdom
The Oath of Allegiance set out in the Promissory Oaths Act 1868 ends with this phrase, and is required to be taken by various office-holders.
United States
The phrase "So help me God" is prescribed in oaths as early as the Judiciary Act of 1789, for U.S. officers other than the President. The act makes the semantic distinction between an affirmation and an oath. The oath, religious in essence, includes the phrase "so help me God" and "[I] swear". The affirmation uses "[I] affirm". Both serve the same purpose and are described as one (i.e. "... solemnly swear, or affirm, that ...")
In the United States, the No Religious Test Clause states that "no religious test shall ever be required as a qualification to any office or public trust under the United States." Still, there are federal oaths which do include the phrase "So help me God", such as for justices and judges in .
Presidential oath
There is no law that requires Presidents to add the words "So help me God" at the end of the oath (or to use a Bible). Some historians maintain that George Washington himself added the phrase to the end of his first oath, setting a precedent for future presidents and continuing what was already established practice in his day and that all Presidents since have used this phrase, according to Marvin Pinkert, executive director of the National Archives Experience. Many other historians reject this story given that "it was not until 65 years after the event that the story that Washington added this phrase first appeared in a published volume" and other witnesses, who were present for the event, did not cite him as having added the phrase. These historians further note that "we have no convincing contemporary evidence that any president said "so help me God" until September 1881, when Chester A. Arthur took the oath after the death of James Garfield." It is demonstrable, however, that those historians are in error regarding their claim that there is no "contemporary evidence" of a president saying "so help me God" until 1881. An eyewitness reporter to Lincoln's second inaugural in 1865 clearly observed Lincoln saying the phrase.
Oath of citizenship
The United States Oath of Citizenship (officially referred to as the "Oath of Allegiance", 8 C.F.R. Part 337 (2008)), taken by all immigrants who wish to become United States citizens, includes the phrase "so help me God"; however provides that the phrase is optional.
Military
The Enlistment oath and officer's Oath of Office both contain this phrase. Normally, it is not required to be said if the speaker has a personal or moral objection, as is true of all oaths administered by the United States government. However, a change in October 2013 to Air Force Instruction 36-2606 made it mandatory to include the phrase during Air Force enlistments/reenlistments. This change has made the instruction "consistent with the language mandated in 10 USC 502". The Air Force announced on September 17, 2014, that it revoked this previous policy change, allowing anyone to omit "so help me God" from the oath.