It follows German Social Democrat leader Sigmar Gabriel's decision not to compete in September's elections. Gabriel said that, considering his party's current poor poll ratings, Schulz stood a better chance of success.
Schulz is now expected to be confirmed as his party's candidate, with the daunting job of trying to stop Angela Merkel from a fourth term as German Chancellor.
Schulz, whose term as Parliament President has only just formally ended, is currently thought to have only a slender chance of winning. The SPD are way behind in the polls, with pundits predicting their best hopes is to form part of another conservative-led 'grand coalition'.
This comes despite one poll last year suggesting that Schulz is as popular as Merkel, with an approval rating of 57 per cent. As the European Socialists' candidate for the presidency of the European Commission in 2014, he came second to the eventual winner, Jean-Claude Juncker.
Among MEPs, the response was mixed.
Schulz's Socialist colleague, Linda McAvan, commented, "I've worked with Martin for many years. He's someone with strong values and is exactly the kind of leader Germany and Europe need in these difficult times."
UK ECR group member Charles Tannock said, "Although Martin Schulz is from a very different political family and views from mine, I admired his period and conduct as President of the European Parliament, where he was a very effective speaker at a very difficult time for the EU.
"On the occasions when I asked for his help he made himself available and always treated me with respect. On a personal rather than partisan basis, I wish him well for the future."
His German colleague Bernd Lucke said, "This has been cleverly arranged by Sigmar Gabriel. The SPD is in a bad state - now the command in the Suicide Squad goes to Martin Schulz and the foreign minister's post, which Schulz had preferred, goes to Gabriel."
Rebecca Harms, a German MEP and former Greens/EFA group co-Chair, said, "Of course, I cannot say whether Martin Schulz will be able to meet the high, and rising, expectations of the Social Democrats.
"I am sure, however, that his candidacy will help the debate in Germany on our future in the European Union. He is someone who takes the people and their questions and doubts about the EU seriously. But he is also someone who can think outside the box and who sees the bigger picture, so people pay attention and listen to him. That is something our society needs, both in a polarised and EU-sceptic debate, and in this election campaign."
Elsewhere, Ukip MEP Bill Etheridge said, "If Schulz acts in Germany as he has for many years in the European Parliament, he will break the rules and constitution to do whatever he likes and he will appoint his cronies to positions of power.
"He is more interested in giving more power to the Socialist party and keeping his pals in jobs than looking after ordinary German people."