Speaking during the committee stage of the Children and Social Work Bill, Lewell-Buck said the government's focus on adoption was "to the detriment of all other forms of care", adding that the time and money the government has spent on adoption is "staggering", pointing to more than 20 policy changes since 2010.
"What the government should be doing is advocating the form of care that is right for every child, not what they believe is right," she said.
Her remarks were made during her failed attempt to convince committee members to abandon a clause in the bill that would require courts and councils to take into account a child's relationship with prospective adopters.
Lewell-Buck says the clause is "a prime example" of the government's "obsession" with adoption, as it would allow the views of prospective adopters to be prioritised over "relatives and other carers".
She added that the clause could also lead to children being prematurely placed with prospective adopters, even before the conclusion of court proceedings.
This, she said, could undermine the child's prospects of going back to birth family or extended family members and friends "who actually love the child and are doing their best to keep that child in their care".
She also argued that the clause could diminish a child's right to a family life, risk the early separation of siblings and inflict "trauma and grief" on family members.
However, her bid to have the clause removed was defeated by eight votes to five by committee members.
Speaking at the committee, children's minister Edward Timpson said the notion that the government "only has eyes for adoption" within children in care policy is "not borne out by the facts".
He said that, in relation to adoption, the government has been trying to tackle the same issues that Tony Blair had attempted to in the 1990s - namely removing barriers to adoption for those where it is the right course and to cut delays to adoption proceedings.
"I don't think it is acceptable that children had to wait 26 months to be adopted," he said.
He added that courts are also already required to "consider the wishes of family members and consider their views".
The committee is yet to discuss the controversial "exemption clause" element of the bill, which would allow councils the chance to opt out of legal requirements around children's social care.
The exemption clause was removed from the draft legislation following a defeat for the government in the House of Lords last month, but the government has vowed to reintroduce it with some modifications.
Further committee stage consideration of the bill is due to take place on 10 January.