Mercedes-Benz, which CEO Ola Källenius called "an export champion in all directions," is among automakers most exposed to President Donald Trump's tariffs.
CEO Thierry Koskas said the ramp-up of the C3 and C3 Aircross, as well as the launch of the C5 Aircross, will help Citroen make up lost ground.
The compact SUV now rides on Stellantis's STLA Medium platform, which gives more room to rear-seat passengers and allows for a full-electric version.
The Dacia Sandero was just 85 sales ahead of the Peugeot 208.
The Future Hybrid Concept from Horse Powertrain includes an internal combustion engine, electric motor and transmission. It could appear in production cars by 2028.
Buyers favored large and compact SUVs, midsize cars and vans of all sizes. The gains came at the expense of compacts and minicars.
The Peugeot 208 was locked in a tight race with the Dacia Sandero and Nissan Qashqai. Big movers included the VW Tiguan and Opel Corsa, while the Tesla Model Y continued to slump.
Despite a new test regime that has raised CO2 figures for plug-in hybrids, the segment roared back to life in March, reversing a long decline and nearly matching the growth rate of BEVs. Sales were led by BYD and VW Group models.
Sales of battery-electric vehicles were up 24 percent for the month; plug-in hybrid sales increased by 20 percent, and Chinese automakers MG, BYD and Chery had impressive gains.
Investors had pushed back against the pay proposal, saying it was undeserved after a year in which Stellantis lost sales and market share, and bled billions in cash.