Catalysts with heteronuclear metal active sites may have high performance in the nitrogen reduction reaction (NRR), and the in‐depth understanding of the reaction mechanisms is crucial for the design of related catalysts. In this work, the dissociative adsorption of N2 on heteronuclear trimetallic MFe2 and M2Fe (M=V, Nb, and Ta) clusters was studied with density functional theory calculations. For each cluster, two reaction paths were studied with N2 initially on M and Fe atoms, respectively. Mayer bond order analysis provides more information on the activation of N−N bonds. M2Fe is generally more reactive than MFe2. The coordination mode of N2 on three metal atoms can be end‐on: end‐on: side‐on (EES) for both MFe2 and M2Fe. In addition, a unique end‐on: side‐on: side‐on (ESS) coordination mode was found for M2Fe, which leads to a higher degree of N−N bond activation. Nb2Fe has the highest reactivity towards N2 when both the transfer of N2 and the dissociation of N−N bonds are taken into account, while Ta‐containing clusters have a superior ability to activate the N−N bond. These results indicate that it is possible to improve the performance of iron‐based catalysts by doping with vanadium group metals.