Initial results from the vote to renew 171 of 348 Senate seats were expected to leave the French president's LREM party with only 20-30 senators, a severe blow to Macron's hopes to increase the party's presence in the upper house from the 29 seats it currently controls.
The LREM lawmakers currently serving switched over to the party when it was formed 17 months ago.
Despite the poor showing, Sunday's election outcome is not expected to undercut Macron's ability to push through his economic reform agenda. The current Senate is positioned as something of a counterweight to Macron but the lower house National Assembly, where Macron has a clear majority, has the final say on legislation. The Senate has the power to delay bills, but in the case of a deadlock the final say goes to the LREM-dominated National Assembly.
French senators are elected by 76,000 local and national lawmakers, not the general public, which put LREM at a significant disadvantage because the party was only formed in April 2016 and is not yet present nationwide.
The vote came after months of falling approval ratings for the 39-year-old head of state. But a new survey Sunday brought some positive news, with a poll published in the Journal du Dimanche newspaper showed 45 percent of respondents approved of his presidency, up from 40 percent last month.
"I can't call it a success," the head of LREM's group in the Senate, François Patriat, admitted as he forecast that final results would show the party with only up to 30 senators.
Les Républicains expected to hold around 150 seats after the election, up from 142 presently.
"It's really good news," said senior party member Bruno Retailleau.
(FRANCE 24 with AFP and REUTERS)