In a ballot of MEPs on Tuesday, he received 86 votes compared with 61 for Belgian deputy Kathleen Van Brempt.
In a statement, Bullmann said he was “honoured to win the trust” of his group, while European Commissioner Pierre Moscovici said he hoped his election would pave the way for the group to “build its unity around a progressive project.”
Bullmann, aged 61, replaces Gianni Pittella, an Italian member who had led the group since July 2014 but stood down to contest the recent Italian elections. Bullmann has been an MEP since 1999.
A member of the economic and monetary affairs committee, he will lead the group into next year’s European elections.
Both Bullmann and Van Brempt had written to MEPs setting out their stalls.
In his pitch, Bullmann said, “We find ourselves at a very particular moment of our common political destiny as a parliamentary group and as politicians fighting relentlessly for a better life for the many.
“Most of our national parties are under intense pressure. Many of our traditional voters and younger generations are losing faith in our capacity to protect and to improve their wellbeing in an ever-faster changing and increasingly volatile world.
“It is my deep conviction that, provided that we stand united, we have all it takes to master our common destiny and to bring social democracy back to full strength. Our aim must be to turn the epochal transformations our civilisation is faced with - such as the sustainability challenge, globalisation and disruptive digitalisation - into drivers for positive change, quality jobs, and wellbeing for all.
“If, once more, we manage to develop a political agenda that credibly and realistically serves this end, social democracy can and will remain our societies’ engine of positive change. In this battle, our S&D group is the progressive movement’s best asset.”
He added, “We are a unique community of extraordinary people, a united diversity of engaged women and men, generations and national backgrounds. I firmly believe that, together, we can make the radical change happen that our societies so desperately need and contribute decisively to the renewal of social democracy, its narrative and policies.
“Being so close to the next European elections, we need to embark on this journey without any undue delay. Most of all, we must continue to believe in our chance to turn the next European elections into a victory for the values of progressive politics.
“Let us start campaigning now, and use every single day to regain our ground, not least through our parliamentary work, but also by fighting beyond the institutional walls. To this end, we should, first and already in April, define a clear plan for the political battles we want to take on and win during the remainder of this parliamentary term. Embedding this set of clear priorities in a far more cohesive political strategy with the PES, with our national parties and our national parliamentary groups must be a key part of this endeavour.”
Bullmann went on, “Secondly, we also need to start preparing strong messages for the upcoming electoral campaign. To be as relevant as possible to our electorates, these should be focused on the fight against economic, social, gender and territorial inequalities, the development of a fair migration agenda, progressive trade, and policies to cater for a healthy environment for all.
“In so doing, we can build on the framework provided by the United Nations Sustainable Development Goals for 2030, which - as our friend Jeffrey Sachs rightly puts it - are in essence social democrat goals paving the way towards a new, fairer and sustainable society,” he told his colleagues.