Sir Paul Terence Callaghan GNZM FRS FRSNZ[1] (/ˈkæləhæn/ KAL-ə-han; 19 August 1947 – 24 March 2012) was a New Zealand physicist who, as the founding director of the MacDiarmid Institute for Advanced Materials and Nanotechnology at Victoria University of Wellington, held the position of Alan MacDiarmid Professor of Physical Sciences and was President of the International Society of Magnetic Resonance.

On his return to New Zealand in 1974, he took up a lecturing position at Massey University, where he began researching the applications of magnetic resonance to the study of soft matter.

The following year, as its founding director, he helped establish the multi-university MacDiarmid Institute for Advanced Materials and Nanotechnology.

Callaghan was President of the Academy Council of the Royal Society of New Zealand (RSNZ), and published over 240 articles in scientific journals, as well as the books Principles of Nuclear Magnetic Resonance Microscopy in 1994 and Translational Dynamics and Magnetic Resonance in 2011.

He was a founding director and shareholder of Magritek,[3] a technology company based in Wellington that sells nuclear magnetic resonance and MRI instruments.

After his death, Callaghan was again recognised with a World Class New Zealand award, becoming the Supreme winner in May 2012.