Smith received the Shield in Johannesburg just before the team prepared to fly to the Caribbean for a prize that has eluded the side since its return to international cricket over 15 years ago.
The South African captain promised his team would work hard to maintain their winning momentum in the mega event.
"This a great honour and a deserved reward for all the hard work the team has put in over the past 18 months," Smith said.
"However, heading the log at this stage will not change our focus on the job at hand over the next two months in the Caribbean," he said.
Smith's side assumed first place from Australia earlier this month following an outstanding run of results over the past year, which has seen the team win 15 of its past 21 matches, including seven of the last eight it has completed.
It is the first time a side has overtaken Australia since the listings began in October 2002.
And if South Africa is still top on April 1 it will win US $175,000 for being there, the side that is placed second at that time will pick up US $75,000.
Cricket South Africa chief Gerald Majola praised Smith for achieving the extraordinary feat.
"This is an outstanding achievement by the Proteas under the leadership of Graeme Smith. The Proteas have had an extraordinary run of form over the past 12 months.
"This includes a 3-2 series win over Australia, sealed by scoring a then world-record 438-9 as well as seven wins from their last eight completed matches," he said.
"Now all eyes are on the (ICC Cricket) World Cup, and the players are quietly confident that their teamwork will stand them in good stead throughout the tournament," he added.
The ICC ODI Championship Shield, produced in late 2002, is circular in shape and weighs approximately six kilograms.
The gold and silver-plated shield depicts in its centerpiece an image of a famous catch taken by South Africa's Jonty Rhodes (dismissing Robert Croft of England during an ODI at Edgbaston in 1998).
The figure, sculpted in sterling silver, is triumphantly capturing a 1.5 carat Argyle diamond that represents the white ball of the ODI game.
This theme of the ball is also created on the rim of the Shield with 14 cast sterling silver cricket balls representing 11 players and three umpires while a glimpse of traditional red leather separates the 24-carat gold and silver-plated dishes.