During his time as a lawyer, Kosmidis served the following positions in his home city of Piraeus.

Director and Columnist of the Newspaper 'Piraeus Echoes'

(1975-1978)

Member of the Board of Directors of the Piraeus Lawyer Association

(1984-1987)

President of the Board of Directors of the Insurance Fund for Maritime Agents and Employees 

(1982-1989)