Proposed by Deputy Andrea Dudley-Owen and seconded by Deputy Robert Prow, Deputy Ferbrache promised to lead with action.
'Not action this week, not action today, but action now,' he said.
'In the last term we were faced with two great challenges, but I have never been afraid to make decisions.'
He stressed the importance of looking after the island's economy, and said anyone who thought 97% of the economy was running efficiently was 'not living in the real economic world'.
'We must not borrow unless we can re-pay it and know exactly what we are borrowing that money for,' he said.
Running against him was Deputy Gavin St Pier, who had been the island's chief minister since 2016.
Both realised the electorate wanted change, and outlined in their own ways how they would see the Assembly changing to reflect this.
Deputy St Pier received 17 votes, to Deputy Ferbrache's 23 in the Assembly's secret ballot.
Tomorrow the Policy & Resources committee will be elected.
Read more in tomorrow's Guernsey Press.