Hewish proposed the construction of a large phased array radio telescope, which could be used to perform a survey at high time resolution, primarily for studying interplanetary scintillation. In 1965 he secured funding to construct his design, the Interplanetary Scintillation Array, at the Mullard Radio Astronomy Observatory (MRAO) outside Cambridge. It was completed in 1967. One of Hewishs PhD students, Jocelyn Bell (later known as Jocelyn Bell Burnell), helped to build the array and was assigned to analyse its output. Bell soon discovered a radio source which was ultimately recognised as the first pulsar. Hewish initially thought that the signal might be radio frequency interference, but it remained at a constant right ascension, which is unlikely for a terrestrial source. The scientific paper announcing the discovery had five authors, Hewishs name being listed first, Bell's second.
Hewish and Ryle were awarded the Nobel Prize in Physics in 1974 for work on the development of radio aperture synthesis and for Hewish's decisive role in the discovery of pulsars. The exclusion of Bell from the Nobel prize was controversial (see Nobel prize controversies). Fellow Cambridge astronomer Fred Hoyle argued that Bell should have received a share of the prize,  although Bell herself stated "it would demean Nobel Prizes if they were awarded to research students, except in very exceptional cases, and I do not believe this is one of them". while Michael Rowan-Robinson later wrote that "Hewish was undoubtedly the major player in the work that led to the discovery, inventing the scintillation technique in 1952, leading the team that built the array and made the discovery, and providing the interpretation".
Hewish was professor of radio astronomy in the Cavendish Laboratory from 1971 to 1989 and head of the MRAO from 1982 to 1988. He developed an association with the Royal Institution in London when it was directed by Sir Lawrence Bragg. In 1965 he was invited to co-deliver the Royal Institution Christmas Lecture on "Exploration of the Universe". He subsequently gave several Friday Evening Discourses and was made a Professor of the Royal Institution in 1977. Hewish was a fellow of Churchill College, Cambridge. He was also a member of the Advisory Council for the Campaign for Science and Engineering.