In a perfect world, writers write. In fact, that's all they do. They spend their days in contemplative repose, labouring over keyboard or notepad, scripting the next plot twist or character embellishment. Real life, of course, is seldom like this. In the real world, writing must be squeezed in between commitments like paying the hydro bill and driving the kids to baseball or ballet.
Examples are legion.
The poet Wallace Stephens was vice-president of an insurance company, Hartford Life. Early in his career, John le Carr was a British spy in Bonn. Dashiell Hammett worked as a private detective. Contemporary novelist Sheri Holman produced her first novel, A Stolen Tongue ,while working in a literary agency, writing in her off hours. Michael Collins has them all beat, hands down.