The state will hire outside attorneys to appeal a judge's decision granting legal recognition to same-sex couples married outside Kentucky.
Beshear's announcement on Tuesday came moments after Attorney General Jack Conway said he would not ask a higher court to review the decision.
Both are Democrats.
Their moves come four days after a federal judge in Louisville gave the state 21 days to implement a ruling overturning a voter-imposed ban on recognizing same-sex unions.
U.S. District Judge John G. Heyburn issued a Feb. 12 opinion that Kentucky's ban on recognizing same-sex marriages violated the Constitution's equal-protection clause in the 14th Amendment because it treated "gay and lesbian persons differently in a way that demeans them."