The pair were there to check on the clean-up and reconstruction efforts after the government released €300 million ($356.5 million) in immediate help to the victims of the worst natural disaster in decades.
Their visit took place exactly three weeks before German voters elect a new parliament, and as Merkel's conservative bloc struggles in the polls. Laschet's image has been hit particularly hard in the immediate aftermath of the floods, when he was caught on camera laughing and joking during a visit to the devastated region.
At the time, the country's president Frank-Walter Steinmeier was giving a solemn tribute to the victims.
How is the region recovering from the floods?
In mid-July, several days of extreme rain triggered severe flooding along rivers in the western states of Rhineland-Palatinate and North Rhine-Westphalia.
A total of around 180 people died in Germany, with dozens of deaths reported in neighboring Belgium.
The German federal and state governments have committed a further €30 billion to rebuild property and infrastructure that was damaged or destroyed in the tragedy.
Reporting from Hagen, DW's Jessie Wingard said residents are not happy with the slow pace of the clean-up.
"Locals in Hagen ... say none of the almost 2,000 businesses in the city are back to full operation since the region was affected by never-before-seen floodwaters," she wrote on Twitter.
One resident told Wingard: "First COVID, now this. We're ruined."
Merkel admitted during a press conference that the reconstruction "will take a long time."
What did Merkel and Laschet do during their visit?
Merkel and Laschet met with local residents whose homes were overwhelmed by floodwaters as well as the colleagues of two volunteer firefighters who had died during rescue operations in the Sauerland.
One of them, a 46-year-old man drowned while rescuing a man who had fallen into the floodwaters; a 52-year-old firefighter collapsed a short time later and also died.
The pair also traveled to Hagen, the site of one of many bridges destroyed in the floods. The rebuilding of the structure is almost complete.
Who is leading the electoral race?
Laschet is the state premier of North-Rhine Westphalia, which was worst affected by the floods.
Both Merkel and Laschet are part of the German conservative bloc that comprises the Christian Democratic Union (CDU) and Bavaria's Christian Socialist Union (CSU). In recent weeks, the bloc has been overtaken in the polls by the center-left Social Democrats (SPD).
The latest survey by INSA published in Bild am Sonntag newspaper on Sunday showed the SPD retaining the lead at 25%, the CDU/CSU down a percentage point to 20% and the climate-friendly Greens in third place on 16%, also a percentage point lower.
Merkel used Sunday's visit to play up her would-be successor's suitability as German leader.
"Armin Laschet is leading this largest state ... very successfully," she said. "And whoever can lead a state like this can also lead the Federal Republic of Germany as chancellor."
mm/dj (AFP, dpa)