There had been disagreement over whether the role of speaker should go to the biggest party, the Social Democrats by a small margin, or to the biggest block, the center-right Alliance.
Last week, the Social Democrats' chief candidate, Björn von Sydow declined to run, because he did not want to be elected with the help of the far-right Sweden Democrats, now in Parliament for the first time.
Then, newspaper Dagens Nyheter reported last week that all the parties had agreed to stand behind the Moderate's candidate, in order to prevent the Sweden Democrats from holding the balance of power in this decision.
However, when Härstedt was named a candidate, the situation changed, leaving the Sweden Democrats holding the balance of power. The Sweden Democrats have confirmed that they chose to lend their 20 votes to support the victor, Westerberg.
The deputy speaker is now a Social Democrat, and the second deputy speaker comes from the Greens, which is the third largest party in parliament. The Sweden Democrats had argued that that post should go to the third biggest "block", and launched their own candidate, who was resoundingly voted down.