Gross domestic product (GDP) grew 11 percent in January-March from the previous quarter, when the economy had contracted 10.8 percent, according to the National Economic and Social Development Board.
GDP rose 0.3 percent compared with the same period in 2011.
The months-long floods last year killed hundreds of people and caused widespread damage to Thailand's industrial heartland north of Bangkok.
Investment by companies to get their plants back up and running is now helping to revive the economy, while the agriculture sector posted solid growth and consumer demand also rebounded in the first quarter, the figure showed.
At their height the floods affected 65 of the country's 77 provinces, deluged hundreds of thousands of homes and forced the closure of large industrial parks, disrupting global supply chains.