After Mrs Merkel’s CDU, its sister party the CSU, and the left-wing SPD agreed an initial programme of government, the vote will determine whether formal coalition negotiations can go ahead.
The coalition is far from a done deal, with some commentators predicting a grassroots uprising against the compromise deal.
However an expert has predicted that if the deal is approved, it could actually be very negative for all of the parties involved.
Matthias Quent, director of the Institute for Democracy and a researcher of right-wing populism, said renewing the grand coalition could leave many German voters dissatisfied.
He told the business newspaper Handelsblatt: “The grand coalition symbolises ‘more of the same’ and is likely to consolidate dissatisfaction among voters who feel unrepresented.”
The cushy consensus building and compromise at the heart of German politics has frustrated many voters, who lashed out in the ballot box in the September election.
The collective vote share of the grand coalition parties fell from 67 percent in 2013 to just 53 percent in 2017 as voters rejected “more of the same”.
Many instead backed more polarised parties with clearer unique identities: AfD, the right-wing Free Democrats, and the left-wing Greens and Die Linke.
Mr Quent spotted an additional problem, in that “so far there is no indication of how the parties want to address the large number of non-voters who are not yet toying with the right-wing radicalism.”
Without a clear strategy for attracting such voters by one of the main parties, it was most likely dissatisfied floating voters would turn to AfD, he explained.
SPD leader Martin Schulz has starkly warned of what could happen to his party if its members do not back the coalition.
He told Der Spiegel: “If the party reject a coalition it will lead to new elections, and fast. If parties who represent a majority in the Bundestag fail to form a new government, they will be punished by the voters.”
However Mr Quent’s predictions suggest the SPD will also be punished by voters if they do build a coalition.
If the agreement is rejected, Germany will either go to the polls again, re-running the September election again in the hopes of achieving a different result, or will bleed by a CDU minority government.
Additional reporting by Monika Pallenberg.