Following the legislative elections later that year, he joined the newly established UDI led by Jean-Louis Borloo and became the spokesperson of its parliamentary group.

[4] In the Republicans’ 2016 presidential primaries, Lagarde and his UDI endorsed Alain Juppé as candidate for the office of President of France.

Amid the Fillon affair, he first called on the candidate to quit the election race in favour of Juppé[7] but eventually suspended the UDI's support for the campaign altogether.

[8][9] Ahead of the Republicans' 2017 leadership election, he announced that the alliance between UDI and LR would end indefinitely in the event of Laurent Wauquiez becoming the party's chairman.

[11] In 2013, Lagarde was – alongside Yves Jégo – one of two UDI members who voted against his parliamentary group's majority and instead supported the legalization of same-sex marriage in France.