Police say about 1,000 protesters, most of them EU treaty opponents, demonstrated outside government buildings where Mr. Sarkozy met with Irish officials.
In a statement, Mr. Sarkozy expressed respect for the results of the Irish referendum. But the French leader, whose country holds the rotating EU presidency, also reaffirmed his commitment to the treaty and expressed satisfaction that the ratification process continues in other EU countries.
Ireland is the only EU member constitutionally required to subject the new treaty to a national vote.
The EU treaty cannot take effect unless every member ratifies it.
The Spanish Senate voted last week to back the treaty. King Juan Carlos' signature would make Spain the 23rd country to have ratified the accord that is intended to replace the draft EU constitution that was rejected by French and Dutch voters in 2005.
Advocates say it remains unclear whether the charter can be salvaged after the Irish defeat.
Some information for this report provided by AP and Reuters.