Among those attending the events will be Mikhail Gorbachev, the former leader of the Soviet Union, and Lech Walesa, who led anti-communist protests in Poland as the head of the Solidarity trade union.
Gordon Brown, the British prime minister, Nicolas Sarkozy, the French president, Dmitry Medvedev, his Russian counterpart, and Hillary Clinton, the US secretary of state, will represent the four nations which occupied post-war Germany.
Events are planned all over the city, including the toppling of 1,000 giant, brightly coloured dominoes along a 1.5km stretch of the wall's original path to symbolise how communist governments in the Eastern Bloc fell one after another in 1989.
A concert will feature performances from Bon Jovi and the Staats kapelle orchestra.
Merkel is reunited Germany's first leader to grow up in
the former Communist east.
The chancellor was working as a scientific researcher in East Berlin when the wall fell.
Merkel said at the weekend that the fall of the wall was "the happiest day in recent Germany history".
Al Jazeera's David Chater, reporting from Berlin, said there was a real sense of celebration in the air.
"But it is nothing like that feeling on the streets on that day in particular, because it marked the end of communism itself."
But for some German residents, the 1990 reunification of the country remains a sore point.
On Saturday, several hundred leftist demonstrators protested against the planned celebrations in Berlin.
A poll of more than 1,000 Germans carried out for the Leipziger Volkszeitung newspaper showed one in eight wanted the wall rebuilt - with the numbers nearly equal in the eastern and western parts of the now-unified country.
Shaken by the mass flight of its citizens into capitalist West Berlin, East Germany began erecting its "anti-fascist protection barrier" in the early hours of August 13, 1961.
According to a study published this year, at least 136 people were killed at the Berlin Wall between 1961 and 1989 while trying to escape.
However, thousands managed to evade the minefields, dogs and guards in watchtowers, using schemes including tunnels, aerial wires and hidden compartments in cars in order to make it to the West.