AbstractCovalent Organic Frameworks (COFs), an emerging class of crystalline porous materials, are a new type of support for grafting lanthanide ions (Ln3+), which can be employed as ratiometric luminescent thermometers. In this work we have shown that COFs co‐grafted with lanthanide ions (Eu3+, Tb3+) and Cu2+ (or potentially other d‐metals) can synchronously be employed both as a nanothermometer and catalyst during a chemical reaction. The performance of the thermometer could be tuned by changing the grafted d‐metal and solvent environment. As a proof of principle, the Glaser coupling reaction was investigated. We show that temperature can be precisely measured during the course of the catalytic reaction using luminescence thermometry. This concept could be potentially easily extended to other catalytic reactions by grafting other d‐metal ions on the Ln@COF platform.