The former EU Commission President added the German Chancellor “sometimes took almost too long”, though did eventually look at issues from a European perspective. Ms Merkel is due to stand down later this year, having held the German premiership since 2005.
Her period in office coincided with a number of EU crises, including the near-collapse of the eurozone in the early 2010s and the migration crisis during 2015-16.
Speaking to German newspaper Der Tagesspiegl, Mr Juncker praised Ms Merkel for being pro-EU, but also criticised her hesitancy.
He commented: “She was hesitant at times, but in the end, she always played the European card.
“Sometimes that took almost too long, but in the end, she found herself among those who worked on future-oriented solutions.
“She has always understood Europe rationally on the basis of the power of the factual, but often thought beyond the present day when making decisions.”
Mr Juncker, who stepped down as EU Commission President in 2019, compared Ms Merkel favourably with her predecessor Gerhard Schröder.
He stated: “In the beginning, Schröder was a lukewarm European.
“Only at the end of his chancellorship did he become wise through experience.”
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Mr Juncker defended Ms Merkel’s handling of the crisis and attacked EU leaders who opposed settling refugees in their countries.
Referring to the Chancellor, he said: “In 2015, she was somewhat speechless when she discovered during the refugee crisis that some were turning their backs and not facing up to their responsibilities.
“In Hungary, Austria and elsewhere, many believed that the refugee drama was a German problem. But it was not a German, but a European problem.
“She has repeatedly emphasised that the richest continent in the world should be able to take in more than a million refugees.
“She had little understanding for those who, often for domestic political reasons, refused to accept this.”
Towards the end of the crisis, in June 2016, Britain voted to leave the European Union.
This finally took place, after a number of delays, in January 2020.
Mr Juncker also revealed Ms Merkel is a “gifted impersonator”.
He said: “We laughed a lot because she showed real talent as a comedian in this regard.
“Don’t ask me now who she parodied.”
Additional reporting by Monika Pallenberg.