Translation:The writer sat in the armchair and started writing.
I have found an answer: http://easyrussian.info/accusative-case-prepositional/
Why use the present participle (writing) when the infinitive (to write) sounds better in English. Is the infinitive писать not imperfective in Russian? Nitpicking I know, but I'm confused when I see the infinitive in Russian translated as a present participle in English.