The Lebanese capital has been left in a disastrous state that has sparked grief and fury, but also global support for Beirut.
"Lebanon is not alone," he tweeted on arrival before pledging Paris would coordinate international relief efforts.
The colossal blast has claimed the lives of 137 casualties, wounded thousands, and caused billions of dollars in damage.
But Macron also warned that Lebanon — already mired in a deep economic crisis, in desperate need of a bailout and hit by political turmoil — would "continue to sink" unless it implements urgent reforms.
Public anger is on the boil over the blast caused by a massive pile of ammonium nitrate that had for years lain in a ramshackle portside warehouse — proof to many Lebanese of the deep rot at the core of their state system.
Macron visited Beirut's harbourside blast zone, now a wasteland of blackened ruins, rubble and charred debris where a 140 meter (460 feet) wide crater has filled with seawater.
As Macron inspected a devastated pharmacy, angry crowds outside vented their fury at their "terrorist" leadership, shouting "revolution" and "the people want an end to the regime!"