Performances of his music were staged around the globe on Friday.
His birthplace of Salzburg, in the foot of the Austrian Alps, led the celebrations for the composer who bequeathed to the world such operas as The Marriage of Figaro, The Magic Flute and
Don Giovanni.
The celebrations in Salzburg ended on a high note on Friday evening, with a concert by classical music superstars, under the baton of Italian conductor Riccardo Muti.
Wolfgang Amadeus Mozart was born on a snowy night on January 27, 1756, to Leopold, a violinist and composer, and Anna Maria Mozart.
By the age of three he was playing on a keyboard and at just five he had written his first composition.
When he died just 35 years later, Mozart had toured the European courts and composed a prodigious body of 630 works including 41 symphonies and 27 piano concertos.
"Mozart remains very current. He knew how to say the indescribable with the simplest of means," the conductor Riccardo Muti told Austrian radio.
All eyes were on Austria, which has seized on the occasion to celebrate its favourite son, also hoping to cash in on his popularity by attracting tourists.
"Mozart would have existed without Salzburg, but Salzburg, this
Salzburg, would not exist without Mozart," the province's governor,
Gabi Burgstaller, told the opening concert.
A host of Mozart merchandise from T-shirts, baseball caps to soft toys and even golf balls have flooded the streets of Salzburg and the Austrian capital, Vienna, angering the likes of Austrian conductor Nikolaus Harnoncourt.
"During this year, Austria is synonymous with Mozart. But this has nothing to do with him," he said.
"I am afraid it is more a matter of money and doing business. We really ought to be ashamed of ourselves rather than being puffed up with pride."
Festivities got under way in Salzburg, with the Vienna Philharmonic striking up a concert at the town's Mozarteum Foundation in the morning.
Later, thousands packed the Kapitelplatz at the foot of Salzburg
Castle for the Vienna Philharmonic concert.
Worldwide the opening chords of the celebrations were heard in
Sydney where from a barge set against the backdrop of the Sydney Opera House, the Sydney Symphony Orchestra performed Mozart's Eine Kleine Nachtmusik and his Divertimento No 11 in D major.
"We are delighted that it falls to Sydney Symphony to kick off the world's first Mozart birthday celebration," said Libby Christie, managing director of the Sydney Symphony Orchestra.
Other landmark events were planned in Beijing and Tokyo, as well as in Berlin, Paris, Prague, London and Vienna.
Mozart's former residence in Vienna was opened after renovation while the house where he composed The Marriage of Figaro has been renamed Mozart's House.