Connecticut already allowed same-sex civil unions that gave largely the same state rights as to married couples, but did not provide the full, federal legal protections of marriage.
The court decided in the 4-3 ruling to overturn the state's ban on gay marriage, saying limiting marriage to heterosexual couples discriminates on the basis of sexual orientation.
"We conclude that, in light of the history of pernicious discrimination faced by gay men and lesbians, and because the institution of marriage carries with it a status and significance that the newly created classification of civil unions does not embody, the segregation of heterosexual and homosexual couples into separate institutions constitutes a cognizable harm," the judges wrote in the majority opinion.
The ruling stemmed from a lawsuit brought in 2004 after eight same-sex couples were denied marriage licenses and sued, saying their constitutional rights to equal protection and due process were violated, reported the Associated Press.
The Supreme Court's decision overturned a lower court's ruling.
"I can't believe it. We're thrilled, we're absolutely overjoyed. We're finally going to be able, after 33 years, to get married," said Janet Peck of Colchester, who was a plaintiff with her partner, Carole Conklin, quoted the AP.
Gov. M. Jodi Rell said Friday that she disagreed, but will not fight the ruling.
"The Supreme Court has spoken," Rell said in a statement. "I do not believe their voice reflects the majority of the people of Connecticut. However, I am also firmly convinced that attempts to reverse this decision -- either legislatively or by amending the state Constitution -- will not meet with success."
But Connecticut House Speaker Jim Amann, a Democrat, said he expects the issue to be taken up by the General Assembly, according to the AP.
"The legislature, as the lawmaking branch of government, debated this issue and made Connecticut one of the few states that offers civil union status for same-sex couples," Amman said.