I've not studied International Relations academically however I often come across people who have similar qualifications as you are considering.
Most work for Governments, NGO's and other international no-profit organisations like the major charities. Only occasionally do I come across such people in the private sector, usually in the field of consulting but every so often some of the multi-nationals will have similarly qualified people.
It's an interesting area but I would view it as complimentary to any existing skills, qualifications or experience you may have. Without a significant additional skill set I can only see it having limited applications and attractions to employers.
Oh one last thing, a willingness to travel and be located in different parts of the world would also be expected