The minimum age to marry or enter a civil partnership is to rise to 18 in England and Wales, as a backbench bill cleared Parliament without opposition.
The bill, put forward last year by Conservative MP Pauline Latham, was approved by the House of Lords on Tuesday with support from government and opposition parties.
It is set to receive Royal Assent and become law later this week.
Until now, people have been able to get married from the age of 16 with parental consent, which campaigners have warned leaves girls, at risk of being coerced into forced marriages.
The law makes it an offence to marry a child and applies to registered marriages and unregistered ceremonial events.
The legal marriage age remains 16 with parental consent in Scotland and Northern Ireland.
Payzee Malika, who was coerced into marriage at age 16, tweeted: “Struggling to put into words what this means. I feel so many emotions. This is real life change.
“This journey has been an incredible one. I’ve worked with so many women who have supported me, one another and this campaign. There is no us without you all. This is for every girl.”
Ms Malika’s sister, Banaz Mahmod, was murdered in 2006 because she ended a violent and abusive forced marriage in a so-called honour killing.
She added: “This morning, my thoughts were clouded with the day I became a child bride. My day started today and that day very early. Anxious both days. Scared both days. Tears both days.
“But today, tears of joy roll down my face because I know what this means for girls like me.”
Ms Latham said she was “thrilled” the bill was “on its way to becoming law.”