The Labour leader has pledged to "embrace the change" after a "very challenging" election day.
Andy McCormick had been expecting his party to win 18 of the new 54-member authority, but after all votes were counted, won only 10.
This included a shock result in Brookvale & Kings Furlong, where two Conservatives won for the first time since 1983, and in the new ward of Winklebury & Manydown.
READ MORE: BDBC results in full
They had been hoping to do well in both areas, but picked up just one out of three councillors in each ward.
There was also trouble in Brighton Hill, which saw his party colleague Kim Taylor fail in her bid to be re-elected, a result which had him worried that he had lost his seat.
READ MORE: BDBC results as they happened
Speaking to The Gazette on Sunday evening, Cllr McCormick said: "It has been a very challenging election, that is obvious.
"There has been a national backdrop, we have got the vaccine bounce, if we look at national and local issues it has been a mixed bag.
"We are disappointed with coming out with fewer [councillors] than we came in with.
"At the same time, we picked up a seat in Brookvale [and Kings Furlong] which had been vacated by the BDI Group.
"We can come out of this holding our heads up high. The Liberal Democrats lost two and BDI Group lost five. It has been a long day and that is down to the national backdrop."
The Conservative victory and overall majority of 12 means that the "opportunity is going to be limited" to defeat the administration's motions, meaning Cllr McCormick is going to focus on convincing the party to change motions before the ever see the council chamber.
"I am quite happy to work with Ken [Rhatigan, council leader] to do that because we have a tonne of work to do.
"We have to put these elections behind us and hit the ground running."
He paid tribute to outgoing councillors including Mark Taylor, Colin Regan and Ruth Cooper, all of whom stood down this year.
"It is sad to see those people go but we will embrace the change."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereLast Updated:
Report this comment Cancel