Welsh is currently the programme director for media and campaigns at the Local Government Association (LGA) and takes up his new role on August 17.
Welsh will report to ATOC's chief executive Michael Roberts.
Welsh is the permanent replacement for Edward Funnell who left unexpectedly in March after six and a half years' service. It is understood that Funnell's departure was somewhat acrimonious with an insider at the time noting that he and chief executive Roberts did not see ‘eye to eye'.
While at the LGA Welsh created and led the first ever national press office for local government, which won PR Week's Public Sector Department of the Year Award in the 2008. Before working for the LGA, Welsh was head of media relations of the London Assembly at the Greater London Authority, which he joined after an extensive career in journalism.
Welsh said: ‘I am really excited to be joining ATOC and building on its first rate work to give the train companies a stronger voice. Railways have shaped and enriched Britain, and the train companies are playing a key part in helping to dig the nation out of recession. Working closely with them, I am eager to help the sector navigate successfully through these turbulent economic and political times.'