Soddy was born in Eastbourne, England, and studied at University College of Wales at Aberystwyth and Oxford University (Merton College). He was a researcher at Oxford from 1898 to 1900.
In 1900 he became a demonstrator in chemistry at McGill University in Montreal, Quebec, Canada, where he worked with Ernest Rutherford on radioactivity. He and Rutherford realized that the anomalous behavior of radioactive elements was due to the fact that they decayed into other elements. This decay also produded alpha, beta, and gamma radiation.
In 1903, with Sir William Ramsay, Soddy verified that the decay of radium produced helium.
From 1904 to 1914, he was a lecturer at the University of Glasgow and while there he showed that uranium decays to radium. It was here also that he showed that a radioactive element may have more than one atomic weight though the chemical properties are identical; this led to the concept of an isotope. Soddy later showed that non-radioactive elements also could have multiple isotopes. In addition he showed that an atom moves lower in atomic number by two places on alpga emission, higher by one place on beta emission. This was a fundamental step toward understanding the relationships among families of radioactive elements.
In 1914 he was appointed to a chair at Aberdeen University, where he worked on research related to World War I.
In 1919 he moved to Oxford University, where, in the period up till 1936, he reorganized the laboratories and the syllabus in chemistry.
He received the 1921 Nobel Prize in chemistry.
He died in Brighton, England.