The vote was unanimous at the extra party meeting in Stockholm, when the former leader Anna Kinberg Batra formally stepped down.
With less than a year to the next election, 53-year-old Kristersson said in his first speech as party leader that his main priority is to reunite the four party Alliance. The Alliance governed Sweden between 2006-2014 and was made up of the Moderates, the Liberals, the Christian Democrats and the Centre Party.
"Ahead of the election I have one crystal clear goal, we will create a new Alliance government. I want that we continue to co-operate with, talk to and compromise with the Alliance. That is where our political history is and that is where our political future awaits," he said.
Kristersson spoke about hope and hard work, and said the party should attract voters back by clearer values and by contributing a new tone in the political debate.
The Moderate Party fell in the opinion polls in the beginning of the year, dropping from roughly 23 per cent to about 16 per cent, after the former leader Anna Kinberg Batra announced that they should be prepared to talk also to the anti-immigration Sweden Democrats.
In a recent poll of polls, carried out after Kinberg Batra announced she was stepping down, only just under 17 per cent of those polled said that they would vote for the Moderates. That can be compared to just over 23 per cent who voted for the party in the election 2014, which at the time was seen as a disappointment.