Same-sex adoption is now legal in Mississippi after a federal judge struck down the state's 16-year old anti-gay adoption law.

Mississippi was the last state to have such a ban on the books after the U.S. Supreme Court's decision last year legalising same-sex marriage.

In a 28-page ruling filed on Thursday, U.S. District Judge Daniel Jordan issued a preliminary injunction against the ban, citing the Supreme Court's decision legalising same-sex marriage nationwide last summer. NBC News reported.

The Supreme Court ruling "foreclosed litigation over laws interfering with the right to marry and rights and responsibilities intertwined with marriage," Jordan stated in his ruling. "It also seems highly unlikely that the same court that held a state cannot ban gay marriage because it would deny benefits — expressly including the right to adopt — would then conclude that married gay couples can be denied that very same benefit."

The court case stemmed from the complaint filed last year by four same-sex couples who were joined by the Campaign for Southern Equality and the Family Equality Council. According to the complaint, hundreds of families and thousands of children in Mississippi were disrespected and denied legitimate rights, benefits and duties that come with legal parentage.

Jordan ruled that denying same-sex couples the right to adopt violated the Equal Protection Clause of the U.S. Constitution.

Various supporters and human rights groups praised the ruling.

"Two sets of our clients have waited many (almost 9 and 16) years to become legal parents to the children they have loved and cared for since birth," said Roberta Kaplan, lead attorney in the case for the Campaign for Southern Equality, a North Carolina-based activist group, which represented four Mississippi couples in the suit along with the Massachusetts-based Family Equality Council.

"We hope that it should finally be clear that discrimination against gay people simply because they are gay violates the Constitution in all 50 states, including Mississippi,'' she added.

Susan Hrostowski, one of the original plaintiffs, said: "Our son just turned 16 on Easter Sunday and is going to get his driver's license tomorrow. For us, the feeling and the way we have operated as a family have never been impacted by this law. But to have this ruling and to be able to start the adoption proceedings tomorrow means everything to me.''

The Human Rights Campaign's Mississippi state director Rob Hill also welcomed the decision, saying it affirms that qualified same-sex couples in Mississippi seeking to become adoptive parents are entitled to equal treatment. "Judge Jordan has repudiated reprehensible efforts by our elected leaders to deny legal rights to our families. They are on the wrong side of history, and today's decision confirms, yet again, that they are also on the wrong side of the law."