He is a member of a number of ensembles including his own critically acclaimed group, Trot A Mouse with Tom Rainey, Ingrid Laubrock and Mat Maneri, world renowned drummer Jim Black's group Smash and Grab with whom Jermyn will soon perform at The Village Vanguard., a collaborative trio with Allison Miller and Jerome Sabbagh, Howard Peach (with Lander Gyslelinck and Chris Speed), as well as his solo project of tape pieces entitled Spirit Spout, commissioned by the PRS for Music Foundation, IMC and Culture Ireland which featured a recent performance at the London Jazz Festival.
Simon regularly performs all around Europe and the States at festivals and clubs.

Of his most recent release entitled "Pictorial Atlas of Mammals" by his band Trot A Mouse, the Irish Times said;

'Saxophonist Ingrid Laubrock, violist Mat Maneri and drummer Tom Rainey may not be troubling the top of the charts, but they represent the vanguard of American improvised music and, with records like this, Simon Jermyn is claiming a place among them.'

and of his previous album entitled "Hymni" Downtown Music Gallery's Bruce Lee Gallanter said; “By far, this is the best solo electric bass effort I’ve heard since Hugh Hopper’s classic solo album ’1984′ from 1973.”

Since moving to New York Simon has had the opportunity to perform with Bill McHenry, Ben Monder, Jim Black, John Hollenbeck, Oscar Noriega, Chris Speed, Tony Malaby,Ralph Alessi, Dan Tepfer, Ches Smith, Loren Stillman, Jonathan Finlayson, Satoshi Takeishi, The Mivos Quartet, Jacob Sacks, Jeff Davis, Briggan Krauss, Tommy Crane, Tyshawn Sorey, Nate Wood, Kirk Knuffke, Empyrean Atlas and Glass Ghost amongst others.

In addition to the above Simon holds a PhD in Performance from University of Ulster.