Gordon Brown joined the campaign trail in Blaenau Gwent and admitted Welsh manufacturers were facing a tough time with competition from China.
But the chancellor said that record investment is transforming the Welsh economy.
The south Wales seat is being fought over after independent MP and AM Peter Law died from a brain tumour in April.
He had overturned a massive Labour majority when he quit the party and ran in protest over women-only shortlists.
Jobs and the future of the Blaenau Gwent economy took centre stage as Mr Brown arrived at the Beaufort Theatre on Wednesday.
More investment and more job opportunities was his main message to representatives of a number of local companies including Continental Teeves which recently experienced job losses.
"In this constituency at the peak of unemployment there were 1,200 young people unemployed and that is down to 200," he said.
The situation, he added, was the same for long term unemployment and the reductions in unemployment made him more determined to help those still out of work.
"These people are still our responsibility and we want to get them back to work," he said.
"Unemployment continues to come down but that is no reason to be anything but determined to bring it down further."
The chancellor went on to highlight that a strong partnership between local companies, the Welsh assembly and the UK Government is essential.
But, he added, there were reasons to be optimistic with the Ebbw Vale rail link and the redevelopment of the old steelworks.
Mr Brown then paid a visit to St Illtyd's primary school in Abertillery where he chatted to those who may hope to reap the benefits of any economic regeneration.
Other parties contesting the poll gave their views on the visit
John Rodgers, from the Blaenau Gwent People's Voice, said: "Gordon has said today that things will keep getting better. I seem to remember that tune when the Labour party got into power. 'Things can only get better', well, they haven't got better in Blaenau Gwent."
Conservative AM Alun Cairns said: "That deprivation still exists after nine-years of a Labour government, after all the promises. It's quite obvious that those policies have failed and are tired."
Liberal Democrat AM Mike German said: "The evidence is there that the economy of Blaenau Gwent is going downhill not going uphill, closures of big factories, job losses and people just don't have the money in their pockets.
Plaid Cymru AM Alun Ffred Jones said: "Blaenau Gwent and the valleys of the south Wales coalfield ruled by Labour for over 80 years and they are among the poorest areas of the United Kingdom, and indeed the whole of Europe, and the Labour party must take responsibility for that."