Many hope that the Global Stocktake under the Paris Agreement can become a catalyst for increased mitigation ambition over time. Based on different theories of change, this paper outlines four governance functions for the Global Stocktake. It can contribute to the Paris Agreement as a pacemaker (stimulating and synchronizing policy processes across governance levels), by ensuring accountability of Parties, by enhancing ambition through benchmarks for action and transformative learning, and by reiterating and refining the guidance and signal provided from the Paris Agreement. The paper further outlines process- and information-related preconditions that would enable an ideal Global Stocktake.