Diamonds that are "clean" will have a new label after key players in the business introduced the "5th C" stamp.
About 2% of diamonds are from conflict zones
The new "ethical" label for diamonds from a conflict-free origin will come into force at the end of the year.
An agreement was signed by Antwerp's federation of diamond dealers, Global Witness, and the association of miners and diamond-cutters (ICM).
Diamonds are already certified by four Cs for carat, colour, clarity and cut, giving an overall measure of quality.
The fifth C will guarantee the stone is not a "blood" diamond, funding war or one that has been mined using child labour.
"It is an important turning point but there is still a lot of work to be done in stamping out illegal trafficking in diamonds," said Alex Yearsley, a spokesman for Global Witness, a non-governmental organisation.
Sales of the stones have dropped from between 15% to 20% in Europe since 1994.
Professionals in the business have been concerned about its image and competition from synthetic diamonds.