With 113 votes in favour and 64 against, the 200-seat house on Thursday opted to allow gays to adopt any biological or adopted children that their partner had before the start of their relationship.
The lower house, or National Council, thus tiptoed in the footsteps of the senate, or State Council, which adopted a far broader measure in March.
Switzerland's largest party, the populist right-wing Swiss People's Party (SVP), had called on the lower house to reject Thursday's motion, insisting children should have a
mother and a father.
"If we accept this Senate motion today, we are opening a Pandora's box," warned SVP's Oskar Freysinger ahead of the vote.
The motion was "radical and goes against nature," agreed Christian Luescher of the Free Democratic Party, which was split down the middle on the issue.
"Nature wants a child to have a father and a mother, not two fathers or two mothers," he insisted.
Other critics in parliament meanwhile said that the change did not go far enough and criticised the chamber for not passing the same motion voted through the upper house of parliament.
That version allowed adoption for all adults, regardless of their lifestyles or marital status.
Socialist Carlos Sommaruga, who voted in favour of Thursday's motion, meanwhile described it as a "first small step" to help children already living with same-sex parents.
He stressed that the current law, which explicitly bans adoption by homosexuals in registered partnerships but not by single gays, was "incoherent" and "leads to distortions and absurd situations."
Cathy Ecoffoy, the co-president of the Swiss association Rainbow Families, also stressed the irony of the current law.
"If you have a God-daughter, for instance, who loses her parents, you are not allowed to adopt her because you are in a partnership," she told AFP.
Although Ecoffoy would have preferred the March motion, she welcomed Thursday's vote as a step in the right direction.
"We enthusiastically hail this vote because it takes into account the reality for children . . . who until now have been raised in an unjust way," she said.
She pointed out that children already living with same-sex couples have no legal rights in relation to their non-biological parent, with for instance no guarantees they can continue living with that person if the biological parent were to die.
Any law change on this issue meanwhile cannot be expected for quite a while.
Thursday's vote means the upper house will now need to vote on the narrower motion and if approved, the government will be asked to draw up a proposal
that will be resubmitted to a new parliamentary vote.
In light of the sensitive nature of the issue, observers say opponents might very well manage to gather the 100,000 signatures needed for it to be put to a national referendum.
Switzerland has since 2005 allowed homosexuals to enter into legally binding registered partnerships, but that law explicitly banned gays in partnerships from adopting.