Colm Mulcahy (born September 1958) is an Irish mathematician, academic, columnist, book author, public outreach speaker, amateur magician and Professor Emeritus at Spelman College.

In addition to algebra, number theory, and geometry, his interests include mathemagical card magic and the culture of mathematics–particularly the contributions of Irish mathematicians and also the works of iconic mathematics writer Martin Gardner.

[9] From January 2021 to December 2024, he was the Chair of Gathering 4 Gardner, Inc.[10] He is the creator and curator of the Annals of Irish Mathematics and Mathematicians.

[13] Much of this work is collected in his book Mathematical Card Magic: Fifty-Two New Effects [14] He has appeared in Brady Haran's Numberphile web series.

Mulcahy is a mainstay of Gathering 4 Gardner (Vice-President 2016-2020, Chair 2021–2024), an organisation formed to honour the wide-ranging contributions made by the celebrated mathematician, skeptic, magician, philosopher, and writer.

[24] In 1997 Mulcahy received the MAA's Allendoerfer Award for excellence in expository writing for a paper on the basics of wavelet image compression.