Leroy "Lee" Cronin FRSE FRSC (born 1 June 1973) is the Regius Chair of Chemistry in the School of Chemistry at the University of Glasgow. He was elected to the Fellowship of the Royal Society of Edinburgh, the Royal Society of Chemistry, and appointed to the Regius Chair of Chemistry in 2013. He was previously the Gardiner Chair, appointed April 2009.

Cronin was awarded BSc (1994) and PhD (1997) from the University of York. From 1997 to 1999, he was a Leverhulme fellow at the University of Edinburgh working with Neil Robertson. From 1999-2000 he worked as an Alexander von Humboldt research fellow in the laboratory of Achim Mueller at the University of Bielefeld (1999–2000). In 2000, he joined the University of Birmingham as a Lecturer in Chemistry, and in 2002 he moved to a similar position at the University of Glasgow.

In 2005, he was promoted to Reader at the University of Glasgow, EPSRC Advanced Fellow followed by promotion to Professor of Chemistry in 2006, and in 2009 became the Gardiner Professor. In 2013, he became the Regius Professor of Chemistry (Glasgow).

Cronin gave the opening lecture at TEDGlobal conference in 2011 in Edinburgh. He outlined the initial steps his team at University of Glasgow is taking to create inorganic biology, life composed of non-carbon-based material.

In 2022 Cronin was suspended by the Royal Society of Chemistry for three months for breaching their code of conduct, following a full independent investigation of a complaint made by a third party.

• 2007 Philip Leverhulme Prize by the Leverhulme Trust
• 2012 Royal Society of Chemistry Corday–Morgan medal
• 2014 recognised as one of the UK's top 10 Inspiring Scientists and Engineers (RISE) as well as being recognised as one of the top 100 UK practising Scientists by the UK Science Council.

• 2015 Royal Society of Edinburgh BP / Hutton Prize for Energy innovation. Royal Society of Chemistry Tilden Prize.

• 2018 American Chemical Society Inorganic Chemistry Lectureship Royal Society of Chemistry Interdisciplinary Prize for his work developing the field of digital chemistry

Cronin was the subject of a film entitled Inorganica, which documents the progress of his research in inorganic biology and origins of life.

In 2012 Cronin was described to be designing robots using 3D printed-architectures to discover and design new chemicals] and also apply this to important drugs By making a modular system he was able to build a programming language for chemistry. This was extended to ensure the chemputer was universal and this was demonstrated by reading the chemistry synthesis literature and converting it into executable chemical code. The emergence of the ontology for digital chemistry required the design of modular hardware, the development of chempilation - the ability to compile chemical code 'XDL code' to any compatible hardware. While this is well established concept in computer science, Cronin and his team were the first to apply this to chemical robotics.

In 2017 Cronin first published the concept of assembly theory which aims to quantify how complex a molecule is but considering how many steps it would take to build the molecule using the minimum number of steps to add together the various parts allowing resuse, and this is called the assembly index. The important thing about the assembly index is that it is experimentally measurable and it was proposed that the assembly index of complex molecules could be a unique way to use complexity as a biosignature. This hypothesis was then demonstrated using mass spectrometry and the use of the theory to explore chemical spaces was expanded with the development of theory. The mathematical formalism of Assembly Theory was then expanded by Cronin in 2022 and the theory expanded to explore how molecular complexity before biological evolution could be used to build a framework to both quantify and explain selection and evolution. In this paper Cronin and his collaborators presented the Assembly Equation where the amount of Assembly 'A' is a function of the assembly index of the object and its copy number. Most recently Cronin has demonstrated that the molecular assembly index is an objectively measurable quantity by measuring the assembly index of molecules using mass spectrometry, infra red and NMR spectroscopy. Assembly theory was explored in a quanta article by Philip Ball, by Carl Zimmer in the New York Times, and also in a popular science book by Sara Walker.

• The Cronin Group
• Cronin biography
• Leroy Cronin at TED
  • Lee Cronin: Making matter come alive, a TED talk (2011)
  • Lee Cronin: Print your own medicine, a TED talk (2012)