Following Merkel's comments, German politicians writing on Twitter called for a vote to be held as soon as possible. Martin Schulz, leader of the Social Democratic Party (SPD) -- the second largest party in parliament -- called for parliament not to wait until after the federal election in September. "We will push through marriage equality in Germany," he tweeted. "This week."
The vote is likely to pass with strong support from other German parties and from some lawmakers within Merkel's CDU. Volker Kauder, leader of the parliamentary group of the ruling CDU faction, called Tuesday for CDU members voting for and against the law to show respect for each other's position, according to NTV. But he also warned that such a sudden vote could lead to a "hasty decision."
Merkel's comments on Monday represent a shift for the German leader and her conservative party, the Christian Democratic Union (CDU), which has opposed same-sex marriage to keep in line with "traditional" family values.
The Chancellor made the comments in response to a question Monday evening at an event in Berlin hosted by women's magazine Brigitte. Asked by a gay man in the audience whether he would be able to refer to his partner as "my husband," Merkel acknowledged the widespread support for gay marriage among German voters -- who will vote soon in federal elections -- and suggested a free vote on same-sex marriage could be held among members of parliament.
The Lesben-und Schwulenverband, Germany's biggest LGBT campaigning group, welcomed Merkel's response in a statement Tuesday.
"The LSVD welcomes the fact that after 15 years of an ideological blockade Mrs Merkel and the Christian Democratic Union are ready to make some progress on the issue of same-sex marriage," the statement said.
"Equal rights for all people are a requirement of our basic law ... We want to live in a country where lesbians and gay men are no longer discriminated against."
Merkel under pressure
Many social media users welcomed Schulz's call for a vote. But some expressed frustration that Merkel is taking action only after 12 years in power and see her announcement as no more than a political tactic.
"Please don't forget who has withheld #Ehefueralle from you for 12 years!" Twitter user Pepper Ann wrote Tuesday. "This has nothing to do with values."
With September's election looming, Merkel has come under increasing pressure on the issue. In the past two weeks her main rivals and potential coalition partners have all come out in support of "Ehe fur alle" (marriage for all).
The left-leaning Green party and the centrist FDP both said that they would not enter into any coalition deal if "Ehe fur alle" was not enshrined in it. The left-leaning Die Linke party has long supported full equality.
And in a speech at the SPD congress on Sunday, Schulz promised that same-sex marriage would be legalized in any government involving his party.
Family "is not only father, mother, child," he told a hall packed full of SPD delegates and supporters. Family is "there wherever people take responsibility for each other."
Of the major parties, only the right-wing Alternative fur Deutschland (AfD) has not voiced support for same-sex marriage -- and Merkel has already ruled out a coalition deal with that party.
Trouble for Merkel's sister party?
Gay rights have long been a controversial issue within the CDU and its more conservative Bavarian sister party, the Christian Social Union (CSU).
During a dispute over tax laws in 2012, 13 members of the CDU spoke out in favor of tax equality for same-sex couples.
"In homosexual partnerships, people take long-term responsibility for each other," Kristina Schroder, then Germany's minister for family affairs and a member of the CDU, told German newspaper Sueddeutsche Zeitung. "They are living conservative values."
But the CSU was strongly against the proposed change. "The marriage of man and woman is under special protection because it is fundamentally oriented toward creating new life. This is not the case in homosexual relationships," the CSU's whip in Germany's parliament, Gerda Hasselfeldt, told ARD television.
The CDU needs the support of the CSU and its traditional, religious voters if it is to win the federal election in September.
But Anja Neundorf, associate professor at the University of Nottingham, thinks that some of those voters may be put off by Merkel's new stance on gay marriage.
They are "much more sensitive to this issue" than other voters, Neundorf said. And some might choose to simply stay at home on polling day, she explained.
Twitter user Maximilan Krah was disappointed by Merkel's comments. "SPD, FDP, Greens have made "Ehe fur alle" a condition for any coalition deal, CDU will also topple," he wrote. "Families with children will lose special protections."
Germany currently lags behind many of its European neighbors when it comes to gay rights. Same-sex couples may enter into a civil union but cannot marry, and they are not allowed to jointly adopt children.
In 2001, the Netherlands was one of the first countries to legalize same-sex marriage. Nearly 20 other countries have followed suit, including Spain, Canada, Argentina, France, the United Kingdom and the United States in 2015.