Marine Le Pen, who is ahead in the polls for the vote’s first round, pressed a pro-Syria, pro-Christian stance on a visit to Lebanon.
The National Front leader aimed to boost her international profile with the trip to the former French protectorate.
Speaking after a meeting with Lebanese Prime Minister Saad Hariri, she said she had told him there is “no viable and workable solution” to the Syrian civil war beyond choosing between President Assad and IS.
Ms Le Pen said: “I clearly explained that in the political picture the least bad option is the politically realistic.
“It appears that Bashar al Assad is evidently today the most reassuring solution for France.”
Lebanon has taken in some 1.2 million Syrian refugees – the equivalent of one-fourth of its own population.
Many of those living in the country as a result of being displaced from Syria are Christians.
Analysts say Ms Le Pen hopes to be seen as a defender of Christians in the Middle East, with a view to winning votes of French citizens in Lebanon and Christians at home.
Ms Le Pen’s position differs widely from official French policy and that of Mr Hariri, who is allied with Saudi Arabia against the Syrian leader.
Lebanon’s President Michel Aoun, whom Ms Le Pen also met, supports Mr Assad and the Iranian-backed Hezbollah working to topple him.