[3] During a protest march from Queen's to the US Consulate, he met John Barry, who convinced him that "the Green Party had a practical agenda of what needed to be changed".

Brian Wilson was successful for the party at the election, and Agnew became his full-time research officer.

[4] At the 2010 United Kingdom general election, he stood in North Down, taking 3.1% of the votes cast.

In January 2011, Agnew was elected as the first leader of the Green Party, beating Cadogan Enright in a postal ballot.

[6] Agnew announced he would step down as the Green Party NI leader from Autumn 2018, citing family reasons.