The petition’s author is Anastasia Sovenko, 24, an English teacher from Zaporizhzhia, in southern Ukraine, who identifies as bisexual. She said she felt compelled to draft the petition after reading an article about heterosexual soldiers rushing to marry their partners before heading to war, and feeling sad, angry and frustrated that same-sex couples did not have that option.

“They won’t be able to visit their soul mate in the hospital if something happens,” Ms. Sovenko said. “If they have a child, then the child will be taken from the parent who’s still alive if it’s not a mom who gave a birth. Because for the law they aren’t relatives. They are just two strangers. And this just could be the last one opportunity in their lives to get married.”

Mr. Zelensky can decline to act on the petition, or endorse it by drafting a gay rights bill and sending it for a vote in Parliament, where his governing Servant of the People Party has a sizable majority. He could also simply pass the issue on to Parliament for debate. Mr. Zelensky’s office did not respond to several requests for comment.

Any attempt to change the law faces a high barrier in Ukraine’s Constitution, which states that “marriage is based on the free consent of a woman and a man.” Amending the Constitution requires a two-thirds of Parliament.