He received his Doctor of Philosophy in 1973 from the Hebrew University.
He served as President of the Hebrew University of Jerusalem, was President of the Association for Symbolic Logic from 1996 to 1998, and is currently the President of the Division for Logic, Methodology and Philosophy of Science and Technology of the International Union for History and Philosophy of Science (DLMPST/IUHPS. 2016-2019). His thesis, On Super Compact Cardinals, was written under the supervision of Azriel Lévy. Magidor obtained several important consistency results on powers of singular cardinals substantially developing the method of forcing.
He generalized the Prikry forcing in order to change the cofinality of a large cardinal to a predetermined regular cardinal.
He proved that the least strongly compact cardinal can be equal to the least measurable cardinal or to the least supercompact cardinal (but not at the same time). Assuming consistency of huge cardinals he constructed models (1977) of set theory with first examples of nonregular ultrafilters over very small cardinals (related to the famous Guilmann Keisler problem concerning existence of nonregular ultrafilters), even with the example of jumping cardinality of ultrapowers.
He proved consistent that is strong limit, but. He even strengthened the condition that is strong limit to that GCH holds below.
This constituted a negative solution to the singular cardinals hypothesis.
Both proofs used the consistency of very large cardinals. Magidor, Matthew Foreman, and Saharon Shelah formulated and proved the consistency of Martin"s maximum, a provably maximal form of Martin"s axiom. Magidor also gave a simple proof of the Jensen and the Dodd-Jensen covering lemmas.
He proved that if 0# does not exist then every primitive recursive closed set of ordinals is the union of countably many sets in.