The hackers used the account to post seven images , mostly explicit cartoons in support of Syrian president Bashar al-Assad, before the account was suspended 35 minutes later.
The attack began at 2.30am BST.
Thomson Reuters is the latest victim among global media firms that have been targeted by the campaign, including the Guardian, Associated Press and CBS in April and the Financial Times and Daily Telegraph in May.
It also hacked the account of satirical news site The Onion, which promptly published a piece called How to prevent your major media site from being hacked.
Twitter has been working with media organisations to secure their accounts, including a rapid response tool that suspends accounts until the hackers are locked out.
Thomson Reuters was contacted for comment.
The Syrian Electronic Army first appeared in 2011 at the start of the anti-Assad revolution, though it is thought to operate from Dubai and be controlled by the Syrian government. Its campaigns have included uploading footage of dead insurgents to YouTube and it briefly wiped $130bn (£85.5bn) off the US stock market when it used a hacked AP Twitter account to claim President Barack Obama had been injured in an explosion.
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image: © Howard Lake