In the Protocol Additional to the Geneva Conventions(GC) of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts (Protocol I), 8 June 1977 it is stated:
Art 47. Mercenaries
A mercenary is any person who:
(a) is specially recruited locally or abroad in order to fight in an armed conflict;
(b) does, in fact, take a direct part in the hostilities;
(c) is motivated to take part in the hostilities essentially by the desire for private gain and, in fact, is promised, by or on behalf of a Party to the conflict, material compensation substantially in excess of that promised or paid to combatants of similar ranks and functions in the armed forces of that Party;
(d) is neither a national of a Party to the conflict nor a resident of territory controlled by a Party to the conflict;
(e) is not a member of the armed forces of a Party to the conflict;
(f) has not been sent by a State which is not a Party to the conflict on official duty as a member of its armed forces.
It should be noted that as many countries including the U.S. are not signatory to the Protocol Additional GC 1977(APGC77). So APGC77 art 47 can best be seen as a guide to what a mercenary is. However without an agreed international definition it is the best around.
Under GC III if a soldier is captured by an enemy, he must be treated as a lawful combatant and therefore a Protected Person which for a soldier is as a Prisoner of War (POW) until the soldier has faced a competent tribunal (GC III Art 5). That tribunal may decide that the person is a mercenary using criteria in APGC77 or some domestic law equivalent. At that point the mercenary becomes an unlawful combatant but they must still be "treated with humanity and, in case of trial, shall not be deprived of the rights of fair and regular trial", because they are still covered by GC IV Art 5. The only exception to GC IV Art 5 is if they are a national of the authority which is holding them but in which case they would not be a mercenary under APGC77 Art 47.d.
If after a regular trial, a captured soldier is found to be a mercenary, then they can expect to be treated as common criminals and may face execution. As they are not POWs they can not expect repatriation at the end of the war. The best known, post World War II, example of this was on June 28 1976 an Angolan court sentenced four mercenaries to death and nine others to prison terms ranging from 16 to 30 years. The three Britons and an American were shot by a firing squad on July 10 1976.
The legal status of civilian contractors depends upon the nature of their work and their nationality in respect of the combatants. But if they have not in fact, taken a direct part in the hostilities (APGC77 Art 47.b) they are not mercenaries and are entitled to the protection of the Geneva Conventions.
The article goes on:
Gurkhas and the French Foreign Legionnaires are not Mercenaries
The two best known units in which nationals of a country serve in another nation's armed forces are the British Brigade of Gurkhas and the French Foreign Legion. Soldiers who serve in these two elite units are not mercenaries.
British Gurkhas are fully integrated soldiers of the British Army. They operate in formed units of the Brigade of Gurkhas and abide by the rules and regulations under which all British soldier serve, (Similar rules apply for Gurkhas serving in Indian Army). French Foreign Legionnaires are in formed units of the French Foreign Legion which is deployed and fights as an organized unit of the French Army. This means that as member of the armed forces of Britain or France then under APGC77 Art 47.e and APGC77 Art 47.f they can not be mercenaries.
This I believe is hypocritical, just because the British government say that the Gurkhas are fully integrated soldiers of the British army. They were not British subjects and certainly were not treated like other british citizens. The Gurkhas home country is not ruled by the British and until (2009) they were not even allowed a British Passport. Clearly the British Government picks and chooses the parts of the law that suites them at the time.
What would happen if the British and French went to war against each other and british subjects were serving in the French Foreign Legionnaire????? That I guess is called treason.
Its also worth noting that many countries including the U.S. are not signatory to the Protocol Additional GC 1977(APGC77), so its not worth the paper its wrote on. In other words you can make up what ever definition you choose to describe a Mercenary, twisting the law around to suite your own situation. Terry Aspinall
(The situation during Occupation of Iraq 2003 – shows how difficult it is to define what a mercenary is. While the United States governed the country any U.S. citizen who worked as a armed guard could not be called a mercenary because they were a national of a Party to the conflict (APGC77 Art 47.d). With the handover of power to the interim Iraqi government it could be argued that unless they declare that they are a resident in Iraq ie a resident of territory controlled by a Party to the conflict (APGC77 Art 47.d), they are now mercenaries. If no trial of the people accused of being mercenaries takes place, then the allegations tend to evaporate in a spiral of accusations, denials and counter accusations. It should be noted that Coalition soldiers in Iraq which are supporting the interim Iraqi government are not mercenaries, because either they are part of the armed forces of a Party to the conflict or they have been sent by a State which is not a Party to the conflict on official duty as a member of its armed forces (APGC77 Art 47.f). Taken from indopedia.org