As a student, she ran for the municipal council of Amsterdam in 1991 as the lead candidate of the Reformed Political League (GPV) – a precursor of the Christian Union.

She served four terms as a councilor, filling the positions of leader of the Christian Union's parliamentary group and vice chairman of the council.

During the 2015 European migrant crisis, Kennedy spoke out against the living conditions of refugees in the Netherlands, and she played a central role in local volunteering for asylum seekers.

They spent four months in the Christian living community L'Abri in Eck en Wiel before moving to the United States in December.

[4][12][13] Unable to find a job in her field of study, Kennedy was employed by a women's shelter and did some secretarial work before setting up a travel agency called Eurotrail, organizing cycling trips in the Netherlands.

[16][17][18] When James became a history professor at the Vrije Universiteit Amsterdam in 2003, the family returned to the Netherlands after spending nine years in the United States,[6] settling in Amersfoort.

[4][22] Kennedy was not elected, but entered in the council on 18 April 2006, when Hans van Daalen vacated his seat to become an alderman in the new municipal executive.

Kennedy was critical of the foundation's plans to replace the collection of abstract constructivist and concrete art by works of local young artists.

She argued in the council that the Mondriaan House should spend €160,000 ($240,000 USD) in subsidies on the acquisition of a climate system such that it could exhibit abstract works of art on loan.

[30][31] After a private party offered money, a compromise was reached between Amersfoort in C and the Mondriaan House under which the abstract art would remain and the climate system would be purchased.

[37][38] As a coalition party, the Christian Union voted in favor of a round of spending cuts totaling €20 million ($30,000,000 USD).

[46] Kennedy proposed to subsidize couples therapy for disadvantaged people, arguing that poverty and hardship resulting from divorces are costly to society.

[48] In 2017, a majority of the council voted in favor of a joint proposal by the party and the CDA to make it possible for troublemakers to be placed in a temporary house.

In an opinion article, Kennedy proposed to convert empty office buildings, schools, and healthcare facilities into cohousing units for refugees to divert demand away from the real estate market.

[66] She already stepped down as parliamentary leader as of the start of the following year in order to focus on her career and on the national election campaign, being succeeded by Hans Bol.

[69][72] After her exit form local politics, Kennedy became a youth care worker for The Salvation Army, and she coordinated the sheltering of Ukrainian refugees following the Russian invasion of Ukraine as a location manager for the municipality.

[24][73] Upon her return to the Netherlands in 2003, Kennedy joined the Christian Union's permanent campaign and the party's women's working group called Inclusief as well as the board of trustees of its think tank.

Together with Arie Slob – a former House member – Kennedy argued that public spaces should not be used to showcase innovative and experimental art, calling such works incomprehensible to the general population.

For her hometown of Amersfoort, she suggested erecting statues of statesman Johan van Oldenbarnevelt (1547–1619) and painter Piet Mondrian (1872–1944), both born in the city.

[85][86][3] Kennedy co-authored a 2009 publication by Christian Union's think tank that called for a raise of the retirement age – contrary to the party's official position – to relieve younger families.

[87][88] In 2012, during the European debt crisis, the Christian Union joined the VVD, the CDA, GroenLinks, and D66 in support of a budget that raised the retirement age from 65 to 67 years after the first Rutte cabinet had fallen.

[89] Kennedy never ran for a Senate seat in the 2015 election, saying she wanted to remain a councilor in Amersfoort in order to deal with new responsibilities that were given to municipalities as part of a decentralization effort.

[92][93] Having assisted previous campaigns, she first participated in an election for the European Parliament in 2019 as the eighth candidate on the shared list Christian Union – Reformed Political Party (CU-SGP).

[90][94] Kennedy previously criticized the Christian Union's 2009 decision to end its cooperation in the European Parliament with the Reformed Political Party (SGP).

[98][99] Following the death of Christian Union Senator Peter Ester on 11 December 2022, Kennedy was appointed as his successor due to her position on the party list during the last election.

Kennedy said that she would focus on helping vulnerable people in society, having a fair distribution of the tax burden, and preventing the government from interfering in the responsibilities of individuals and organizations.