"This is due to the fact that many people believe that Angela Merkel in Germany has done a good job but that she is a little bit tired," he added.

"It is incredible how Martin Schulz has changed the situation of the Social Democrats," said Thomas Oppermann, the chief whip of the SPD told CNBC.

The extraordinary party convention took place in the east of Berlin with rainy weather adding to a depressed feeling outside. But inside, the hall was buzzing with banners everywhere and an excited crowd.

The winds of change were palpable in the rather low-key red brick Berlin Arena on Sunday, where the center-left Social Democrats (SPD) voted overwhelmingly for Martin Schulz to be their candidate for the next German chancellor.

At the event, people carried banners with "Jetzt ist Schulz" ("now it's Schulz" which is a play of words with the German saying "now it's enough"). The crowd vigorously cheered the headline speech from Schulz who continuously stressed that he wants more justice and fairness in the country. Party delegates also officially backed him as their party leader on Sunday with Schulz getting 100 percent of the vote.

"We want the SPD to be the strongest political power in Germany," Schulz said. "And I want to be the next chancellor of Germany," he added before several minutes of clapping and cheering from the audience.

What would have sounded like a joke only three months ago - when the approval ratings of the SPD were around 20 percent - it's now a real possibility the party will prove successful with it neck-and-neck against Angela Merkel's CDU (Christian Democratic Union) in all the latest polls.

With the slogan "time for more fairness" and a pledge to reinstate social justice in Germany, Schulz tries to appeal to non-voters but also those who feel disenfranchised with the current political system. He has promised to roll back elements of the so-called Agenda 2010, which laid the foundation for the economic recovery Germany has seen since the early 2000s.

Schulz is currently modelling himself as an ordinary everyday man who got a second chance after being addicted to alcohol.

"Martin Schulz is somebody with a clear attitude, with a fantastic authenticity. He is able to talk to the people and to touch people," Oppermann told CNBC.

Germany is set to hold its federal election on Sunday 24, September.

