"The victory was resounding, crushing and without parallel in the history of our America," read the brief message published in the online edition of the Communist Party daily Granma.
"The oppressed peoples of the world will always be grateful for the strategy and the courage with which you unleashed such a difficult battle of ideas," said the message signed with the 80-year-old leader's name.
He added, "The Cuban people are happy" and sent his good friend and political ally a "very strong" hug.
Venezuelan election officials announced late Monday that ballots from 90 percent of polling stations counted so far showed Chavez leading by 62 percent to 37 percent over his challenger, Manuel Rosales. The message was the first said to be from Castro since last week when he sent his regrets to luminaries from throughout Latin America who traveled to Cuba for his belated birthday celebration.
Castro provisionally ceded power to his brother, Defense Minister Raul Castro, on July 31 after announcing he had undergone surgery for sustained intestinal bleeding.
At the time, he asked that celebrations planned for his birthday on Aug. 13 be postponed to last Saturday to coincide with the 50th anniversary of the Cuban Revolutionary Armed Forces.
Castro also failed to show at a military parade Saturday marking the armed forces' anniversary, disappointing many of the tens of thousands of loyalists there who had hoped that Castro would make at least a brief appearance after an absence of more than four months from the public scene.
The elder Castro's failure to appear raised new questions about whether he will return to power after ruling more than 47 years before falling ill.
Instead, 75-year-old Raul Castro oversaw the parade of troops and military hardware, giving a speech in which he offered to negotiate Cuba's differences with the United States on equal terms.
The U.S. State Department immediately shot down the offer, saying the American government will not open a dialogue with Cuba until it releases political prisoners and holds free elections.