GM Europe owns Vauxhall and the German-based Opel.
Lord Mandelson said that Magna had made it clear that they were committed to continued production in the UK.
He added he would be seeking a meeting to "reinforce that commitment".
Lord Mandelson was speaking after reports that Magna had reached an agreement in principle to rescue GM Europe.
"It looks as if GM in Europe can be saved, it can be turned around," he told the BBC.
-- due to the hugely increased level of spam please make the obvious adjustment to my email address