But the party has deferred choosing his deputy until at least May 8 after an extended meeting in the NSW parliament on Friday.
Mr Speakman's main competition came from former minister and right factionist Anthony Roberts but the former attorney-general was a clear winner, 22 votes to 13.
In his first comments as leader, he said the party would continue with its timeless values while addressing modern issues, namely those affecting youth, women and the environment.
"The Liberal party federally and in NSW has had a number of setbacks in the past 18 months but we remain a party with timeless values," he told reporters.
"We are the party of opportunity, aspiration and reward for initiative."
The Cambridge-educated MP from Cronulla ran on a unity ticket with two upper house MPs, conservative Damien Tudehope and moderate Natalie Ward.
Mr Tudehope was re-elected as Liberal leader in the upper house while Ms Ward was elected to the role of deputy leader in the upper house.
Newly-elected party whips, Chris Rath and Adam Crouch, told reporters the party had got behind their new leader on Friday.
"I'm pleased with these results. It was a very strong result for Mr Speakman," Mr Crouch said on Friday.
The party deferred choosing a deputy leader until May 8, as it considers changing a rule that would allow upper house MPs to contest the position.
This would open the door for Ms Ward, a former roads and women's safety minister internally touted as a future Liberal leader, to run for the role.
Former environment minister James Griffin earlier backed Mr Speakman as the best man to hold the new Labor government to account.
Former deputy leader and moderate powerbroker Matt Kean arrived at parliament with Mr Rath, both declining to say who they would support.
Conservative western Sydney MP Tanya Davies had been tipped to run for the deputy leadership on a platform of recapturing suburban Sydney seats lost to Labor.
The Badgerys Creek MP made headlines last year when she caught COVID-19 after speaking at a rally against vaccine mandates outside the state parliament.
North Shore MP Felicity Wilson had also been expected to nominate for the position.
Premier Chris Minns said he had a shared responsibility to work with the new opposition leader to guide policy decisions and improve the state.
"All I care about is making NSW as good as it can be ... so I take the position seriously, it's a very difficult job," Mr Minns told reporters on Thursday.
Earlier this month, junior coalition partner the NSW Nationals re-elected leader Paul Toole and deputy Bronnie Taylor during their own party room meeting.
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