Gauck, expected to be raised to the largely ceremonial post in the coming weeks after winning backing from all major political parties, replaces Christian Wulff, who resigned Friday amid a series of impropriety allegations.
Hailed as "the president of hearts" by the top-selling Bild daily, the popular, grey haired, genial and softly-spoken East German was a leading figure in the peaceful revolution that brought down the Berlin Wall in 1989.
Born in 1940 in Rostock in the north-east of Germany, Gauck received an early lesson in tyranny when his father was arrested and sent to a Siberian gulag after being sentenced to 25 years by a Russian military tribunal.
Thwarted in his dream of becoming a journalist when he failed to secure a place to study German, Gauck instead studied theology, entered the Church in 1965 and was ordained in 1967.
He once told an interviewer that "at the age of nine, I knew socialism was an unjust system" and he used the pulpit to preach human rights and freedom, quickly drawing attention from the authorities.
When the first protests began that would eventually lead to the fall of the Berlin Wall, Gauck became the spokesman of the "New Forum" in Rostock, an opposition movement that demanded democratic reforms.
And when Germany was reunified amid joyous scenes in October 1990, the man who was formerly closely watched by the hated Stasi secret police was placed in charge of sorting through and opening access to their millions of files.
He served there until 2000, earning respect for balancing the causes of truth and reconciliation as the country again became one.
Describing himself as a "conservative from the liberal left", Gauck appeals to all sides of the political spectrum in Germany and to the people themselves, over half of whom wanted to see him as president, according to recent polls.
As a candidate for the post in 2010, the two most influential media outlets in the country, newsweekly Spiegel and Bild, described him respectively as "the better president" and "the president of hearts."
However, he lost that election to Chancellor Angela Merkel's handpicked candidate for the post, Christian Wulff, who became embroiled in scandal and was eventually forced from office under a prosecutor's investigation.
Prosecutors in Lower Saxony state where Wulff was formerly premier said Thursday they had taken the unprecedented move of asking parliament to lift his immunity to probe allegations he enjoyed favours from a film producer friend.
In the wake of Wulff's resignation, Merkel sought a candidate to unite the parties and eventually bowed to pressure from the opposition and her coalition partners to plump for Gauck, supported by the opposition in 2010.
Merkel, the daughter of a Protestant pastor who like Gauck grew up in communist East Germany, hailed him as a "true teacher of democracy" who had helped the country come together since its reunification in 1990.
For his part, the visibly moved father-of-four who lives with his long-term partner Daniela Schadt, confessed he was "overwhelmed and a little confused" at his nomination, which has to be rubber-stamped by a special parliamentary body.
"It is a very special day for me, even in a life where I have had several," he told reporters.
He said he was pleased that "someone like me, born during a terrible war and who lived 50 years under a dictatorship ... should be called upon today to become head of state."
He added he now wanted to help restore Germans' "faith in their own strength" in the face of the eurozone crisis.
However, he sought immediately to play down expectations, saying he was "neither Superman nor a man without fault."
The media, most of which have run a constant barrage of negative stories about Wulff, were jubilant.
"It is a breath of fresh air for German politics, and Gauck presents an opportunity for a new style of politics," opined Bild.
ZDF television said that Gauck "can save the presidency with his personality" and praised Merkel for her about-face.
"Two East Germans at the top of the federal republic. That is almost a political miracle," said ZDF.