Michael Harris is an internationally renowned expert in the theories of automorphic forms, Shimura varieties, and Galois representations, and his research has ranged over a wide range of topics related to these fields of investigation.

In some of Harris’s earliest work he introduced Iwasawa-theoretic techniques in the context of non-abelian p-adic Lie groups, techniques which are now very topical due to the widespread interest in non-commutative Iwasawa theory and the p-adic Langlands program. In other early work, he initiated the study of automorphic vector bundles on Shimura varieties, including the study of their canonical models and their cohomology, thus opening up an important technique for the study of the arithmetic of automorphic forms on general Shimura varieties. He applied this technique, and others, to make a detailed study of L-functions attached to automorphic forms in a range of contexts, verifying various rationality conjectures of Deligne in many situations.

Together with Richard Taylor, in 1999 he proved the local Langlands conjecture for GLn, and also constructed n-dimensional global Galois representations attached to self-dual cuspforms on GLn over totally real and CM fields. Building on this work came a series of papers, joint with Taylor and other collaborators (Clozel, Shepherd-Barron, Barnet-Lamb, and Geraghty), which served to establish the Sato–Tate conjecture for modular forms, and more generally initiated a framework for studying in the context of n-dimensional Galois representations problems which had previously been approachable only in the more classical setting of two-dimensional representations. In part as a means of encouraging number-theorists to take advantage of this new framework, Harris led the so-called “Paris book project”, a series of volumes dedicated to explaining aspects of theory of automorphic forms on unitary groups, including the stable trace formula, the proof by Laumon and Ngo of the fundamental lemma for unitary groups, and functoriality between unitary groups and GLn with the goal of explaining to number theorists the results that are available in the n-dimensional context.

Harris’s research achievements have earned him numerous prizes and honours, including being an invited speaker at the 2002 ICM in Beijing, winning the Grand Prix Scientifique de la Fondation Simone, and the Clay Research Award, shared with Richard Taylor, in 2007.