President Peter Mutharika approves a law which lifts the age for marriage from 16 to 18.
Human rights activists had pushed for the law, saying Malawi had one of the highest rates of child marriage in the world.
Parliament passed the law two months ago, despite strong opposition from traditionalists.
Rights campaigner Milliam Chilemba welcomed the ban.
“Once they reach puberty, parents consider their girls as adults ready for marriage.”
“Many parents cannot afford to pay school fees for their girls and they opt to marry off their children to relieve themselves of the burden”
This is the reality of life for girls in Malawi.