Jim Murphy has been elected the new leader of the Scottish Labour party, pledging to make Scotland “the fairest nation on the planet” and insisting that he will not lose a single seat to the SNP in May’s general election.

The results gave the MP for East Renfrewshire and former Scottish secretary, always the frontrunner in the contest, a convincing victory over his rival, Neil Findlay.

Murphy described his election as “a fresh start” for Scottish Labour. “A new generation is in charge,” he told the party gathering in Glasgow, echoing the words of MSP Kezia Dugdale, who was announced as the new deputy leader. “But it’s only the beginning. Scotland is changing and so too is Scottish Labour.”

Murphy won 55.77% of the vote, which is equally divided between parliamentarians, members, and union affiliates in an electoral college system, with Findlay winning 34.99% and the former Holyrood transport minister Sarah Boyack taking 9.24%.

Although Findlay received the backing of a number of larger unions, including Unite and Unison, he performed far worse in that section of the electoral college than expected, taking just over half of the available votes while Murphy polled at around 40%.

In his acceptance speech, Murphy called for unity in the party and across the country.

Speaking to Labour voters who supported independence in the referendum, he urged them: “Know this: I share far more with many of you who voted yes than I do with some of the political leaders who campaigned for no.”

Asked later how he planned to reach disaffected Labour supporters, he said that he believed many of those who voted yes would be surprised by how ambitious Scottish Labour is about the further powers to Holyrood recommended in the Smith Commission.

“I’m not trying to convince them that they were wrong,” he said. “I’m not going to try to rerun the referendum. We had that vote and we were on different sides of that one vote on that one day, but let’s now work together on social justice.”

The challenge for himself and Dugdale was: “How do we make Scotland the fairest nation on the planet?”

Acknowledging the amount of work facing him before the general election, with Labour trailing in the polls compared with a surge in support for the SNP, he said that polls “are there to be proved wrong”.

“I know there’s a huge amount of work to do in a really short period of time,” Murphy said. “I am confident that we will hold all [the Westminster seats] that we have. Any seat that the SNP tries to win from Labour increases the chance of David Cameron having an overall majority and I’m determined that won’t happen. We’ve had one referendum and we’re going to have another referendum in May, and it’s on whether Scotland genuinely wants rid of David Cameron.”

Although Murphy promised to give up his Westminster seat for Holyrood if elected, he refused to confirm his plans for finding a seat in the Scottish parliament, repeating that his aim was to be Labour’s candidate for first minister in 2016 and saying that he would make his plans clearer in the new year.

Insisting that it was not important to him whether people voted for him or not, he said that he would build a “team of all Labour’s talents”, as well as bringing in economists and specialists from outside the party. He said that he would also build “a coalition of voters – those who voted yes, those who are aspirational and who want to build a stronger economy”.

He said that the leadership contest had been energising for the party. “Scottish Labour members, trade union supporters and politicians want a return to winning Labour. I’m not worried whether people are leftwing, Labour rightwing, old Labour or new Labour, I just want a return to principled winning Labour.”

Support for the SNP has surged to record levels and a majority are in favour of independence, says a YouGov poll.

Some 47% of people in Scotland intend to vote SNP, against 27% who will vote Labour, 16% who will vote Tory and just 3% backing the Lib Dems.

The SNP’s support is up 27% on its 2010 figure.