The new president was elected by a parliamentary assembly made up of 1,260 MPs and representatives of Germany's 16 states.
'He is the right man at the right time, ' said former foreign minister Gerhard Schröder, Steinmeier's former mentor, in reference to the election of his former disciple in his new post, which he will take after being foreign minister.
Steinmeier was born on January 5, 1956 in the city of Detmold, Germany.
The German president has little executive power but is considered an important moral authority.
Steinmeier is normally studiously diplomatic, but he strongly criticized Donald Trump during the USA election campaign.
Merkel, once uncontested as Germany's most popular politician, has recently struggled against criticism over her refugee policy, including from her own party. "Nothing will be easier, many things will become more hard".
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His election coincided with a Social Democratic surge in polls since the center-left chose Martin Schulz, a former president of the European Parliament, to lead them into battle against Ms. Merkel in the elections.
Mr Steinmeier, Germany's former foreign minister, strongly criticised Donald Trump during the U.S. election campaign.
In his acceptance speech, Frank-Walter Steinmeier, 61, said Germany should be an "anchor of hope" while democratic institutions were under threat across the globe. Steinmeier later became the country's vice chancellor for two years before being crushed by Merkel when he ran for chancellor in 2009.
"For Germany's Social Democrats, Steinmeier's election is a prelude to something bigger to come: a victory in September's elections against Merkel", said Broening.
"It is hardly surprising that Steinmeier has branded himself as the essential anti-Trump", he added.