Anna Homsi campaigned for a war widow's pension
Unmarried partners of any British service personnel killed in the war against Iraq will get pensions, the Ministry of Defence has said.
Under existing legislation, only the legal spouses of military personnel who die in active service are entitled to a MoD pension.
The decision will apply to both heterosexual couples and same sex partners and will be offered when a loved one is killed in "conflict".
Entitlement to a pension will be awarded to partners where there was a "substantial relationship" and eligibility would be judged depending on a range of criteria from financial interdependence, children and shared commitments.
Figures released by the Office for National Statistics on Thursday show the number of marriages in England and Wales has fallen to its lowest level in more than 100 years.
MoD would consider:
Shared commitments, such as mortgages
Prime beneficiary of the will
Length of the relationship
No legal spouse
"The decision would be based on a broad assessment of the substance of the relationship and not all of these criteria would need to be met for entitlement to exist," the statement said.
There has been a cross-party campaign aimed at equalising pension rights in the Armed Forces.
The MoD said the announcement would not affect existing compensation given to all children of military personnel killed in action.
The issue was raised when the MoD refused a war widow's pension to Anna Homsi, the partner of an SAS trooper killed in Sierra
Ms Homsi was pregnant with their daughter, Georgia, when Brad Tinnion, 28, with whom she had lived for seven years, died in action.
Miss Homsi had considered suing the MoD over the matter after she was refused a war pension.
The MoD eventually made a one-off payment of £250,000.