Ferrard joined the Socialist Party in 1980 and was elected as the councillor in the township of Carhaix-Plouguer in 1998 as his first elected office. In the municipal elections in 2001 and 2008, Ferrand lost in both times, obtaining 31% of the vote in 2008. In the 2010 regional elections, Ferrard was one of the PS nominees for the Finistère department. He became councillor for the region on 21 March 2010 and has since chaired the socialist and related group. In 2007, Ferrand ran for Finistère's 6th constituency under the PS banner. He lost to Christian Ménard who achieved 50.19% of the vote. In 2012, Ferrand ran in the same constituency for PS where he got 32.2% of the vote in the first round and then 58.3% of the vote in the second round.
National Assembly
In the National Assembly, Ferrand was a member of the SER group and sits on the Social Affairs Committee. He has never worked in the agricultural or agri-food sector, but is co-chairman of the agricultural and agro-food industries group. He particularly involves himself in social issues and the use of cheaper labour than currently available. While on the Social Affairs Committee, Ferrand was an EU-appointed rapporteur on resolutions around workers and the use of cheaper European labor. In his report, he stated that European workers feel detached due to the lack of social cohesion and the use of cheaper labour to replace them. He advocates measures to limit the replacement of workers. Despite Ferrand's opposition to the Bonnets Rouges movement against the eco-tax, which was started by the Fillon government and further expanded upon by the Ayrault government, he took a stand against the expansions, saying they underline the complexity of the tax system. He supports amendments to the eco-tax. After there was a postponement of the eco-tax, Ferrand and other Breton politicians asked Minister of Energy, Ségolène Royal to rethink the tax plan. On 3 October 2014, the Prime Minister Manuel Valls appointed Ferrard along with the minister of economy, Emmanuel Macron to work on a plan to reform regulations based around labour. He was tasked with looking at the "legal framework that restricts labour from developing" while paying attention to the different situations from many different regions. After consulting many trade unions, experts and other associations, he submitted the report that stresses that reforming the regulated labor market is needed but "reform, don't break, this includes twenty-eight proposals that are aimed particularly at promoting young people's access to the job market." This reform was eventually put to the National Assembly where it was amended by the members of the assembly which resulted in the "Act for Growth, Activity and Equal Opportunity" or the which was lobbied against by unions and other organizations. Ferrand was then appointed as the general rapporteur, one of the biggest reforms within the first five years of President Hollande's term with over 300 articles and sectors such as: transport, savings, labor courts, housings and qualified professions being reformed. More than one hundred and eleven hours went into debate in the National Assembly over the reform. The text was eventually adopted including measures that were originally not there but added during parliamentary debate such as: Letting commercial stores open on Sundays, liberalization of transport services and encouraging qualified professions to allow young people into the profession.
On 16 October 2016, Ferrand was appointed General Secretary of En Marche! by Emmanuel Macron, someone he worked with closely when he was the minister for Economy. The following month, he resigned from leading the PS group in the regional council for Finistère, and confirmed that he quit the PS on 9 May 2017.
Leader of the REM group in the National Assembly
On 24 June 2017, it was announced that Ferrand was officially elected leader of La République En Marche! group in the National Assembly with 306 votes and 2 abstentions.
