Will Portman tweeted Friday that he is "especially proud of my dad today."
Gingrich acknowledged on CNN's "Starting Point" that when an immediate family member reveals that he or she is gay, there are typically three responses.
"You can say, 'I believe my principles so much, I'm kicking you out.' You can say, 'I still believe in my principles, but I love you.' Or you can say, 'Gee, I love you so much, I am changing my principles,'" Gingrich said. "Rob picked the third path. That's his prerogative."
The former presidential candidate stands by his own belief that a marriage is between a man and a woman, and argued the traditional definition will stay in place "no matter what politicians" do.
"I don't think they have the power to change what is a religiously inspired definition," Gingrich said.
Former Pennsylvania Sen. Rick Santorum, a social conservative who ran for president in 2012, said Portman's about-face was personal and doesn't reflect the party's broader direction on social values.
"I'm not too sure the rationale behind what Senator Portman's doing is something that has broad application to the base," Santorum told CNN. "The fundamental principles that attach to the institution of marriage really haven't changed as a result of that personal story. We need to look at what's right, what's right for the American public and more importantly, what's right for children. So we need to try and fight for those things."
Rimmerman said it will be up to younger conservatives who support same-sex marriage to help change views within the GOP.
"It's going to take younger conservative voters to send a message to their party elders that that message is unacceptable," he said.
Some on the right, however, applauded Portman's decision.
Gregory T. Angelo, executive director of the Log Cabin Republicans, said in a statement "if there was any doubt that the conservative logjam on the issue of civil marriage for committed gay and lesbian couples has broken, Senator Portman's support for the freedom to marry has erased it."
"(His) evolution on this issue highlights how personal it is for Americans -- whether they're the junior senator from Ohio or your next-door neighbor, all Americans have a gay friend, colleague or family member, and understand them to be as deserving as their straight counterparts of the inalienable rights of life, liberty, and the pursuit of happiness that are the promise of the United States," Angelo continued.