If you are a citizen of a country that is not a part of the EU and you want to work in Sweden, you must have a work permit. If you plan to work in Sweden for longer than three months you will also need a residence permit. You need a work permit whether you are employed in Sweden or abroad. Even workers posted from another country that move within a company group to work must have a work permit.
For work that is shorter than three months, citizens in some countries must have an entry visa, see link in the right column. There are exemptions from the requirement to hold a work permit for certain work categories who only plan to work in Sweden for a short time.
Source – Migrationsverket, Sweden