In a statement on Tuesday, the ratings agency said a prolonged and intensified political impasse could eventually impair Thailand's economic performance relative to its rating peers, which could undermine its credit strength.
Fitch rated Thailand's sovereign credit rating at BBB+.
The inconclusive election of Feb 2 has failed to ease the recent escalation in political tension.
Political turmoil is not new, and a degree of volatility is factored into the sovereign rating.
The economy has withstood the political rupture since 2006 and other shocks including large-scale flooding in late 2011. GDP growth averaged 2.9% a year from 2008-13, slightly higher than its ratings peer average of 2.6%.
Slackening activity has prompted a substantial two-percentage-point reduction in the authorities' GDP growth estimates for 2014 to about 3%, and the maintenance of an "accommodative stance" in monetary policy.
The international ratings agency expects the economy will bounce back when political tensions eventually ease, underpinning its expectation of 3.5% growth in 2014.
A much sharper and more prolonged slowdown than Fitch currently expects could hurt the banking system via a deterioration in asset quality. However, the risk of political turmoil leading to pressure on external liquidity remains remote.
The Thai stock market yesterday tracked the global stock market's rout after data showing weaker-than-expected growth in US manufacturing, slipping 1.24% to close the market at 1,276.84 points with lacklustre trade worth 25 billion baht.
Big market cap stocks were at the centre of the sell-off.
Political deadlock at home following Sunday's poll also weighed on market sentiment. Foreign investors yesterday yanked 4.89 billion baht out of the Thai stock market, adding their net sales to 21.6 billion year-to-date.
Poranee Thongyen, the research manager at Asia Plus Securities, said the prolonged political turmoil is taking a toll on the country's economic growth.
Foreign investors have sold Thai stocks substantially over the past seven trading days with a net amount of 16 billion baht.
However, export-related stocks are expected to gain as they enjoy the baht's weakness against the US dollar.