The law listed FGM as a criminal offence, along with threats and acts of physical and sexual violence, and emotional abuse, when it was first submitted to lawmakers last September.
Yet opposition from several politicians in April led to the FGM provision being removed from the bill, which was passed into law last week, according to women's rights campaigners.
"It's extremely frustrating that the domestic violence bill was due to include an FGM ban, then a weaker ban and now no ban at all," said Mary Wandia of the rights group Equality Now.
"This is seemingly due to resistance by secret societies, but there is no excuse for continuing to fail Liberian girls," she told the Thomson Reuters Foundation by phone from London.
FGM affects an estimated 140 million girls and women across a swathe of Africa and parts of the Middle East and Asia, and is seen as a gateway to marriage and a way of preserving a girl's purity. It causes numerous health problems that can be fatal.
Half of Liberian women have been subjected to FGM, and four in 10 support the practice in a country where it is carried out by all but a few tribes, and by both Muslim and Christian communities, according to the U.N. children's agency (UNICEF).
It is practised in the West African nation during traditional initiation ceremonies in bush schools, overseen by an immensely powerful women's secret society called the Sande.
While FGM contravenes human rights treaties to which Liberia is a party, campaigners say the government has been reluctant to take a stand because of the Sande's political clout.
FGM may have been removed from the bill due to fears over the impact on hopefuls for next year's elections, said Tamba Johnson of the Women of Liberia Peace Network (WOLPNET).
"If the bill had been passed with the FGM component, politicians seeking votes would perhaps have lost support from the more traditional communities," Johnson said from Monrovia.
Liberia's President Ellen Johnson Sirleaf said at an event on gender equality in the United States last year that her government was committed to introducing a law to ban FGM.
"President Johnson Sirleaf has committed to doing this many times, but we are still waiting," Wandia of Equality Now said.
Nigeria and Gambia banned the practice last year but FGM remains legal in Mali and Sierra Leone.
By Kieran Guilbert
Source: Thomson Reuters Foundation