In local politics, he was first elected to Cavan County Council in 1985 but lost his seat in 1991.

As a result of Fianna Fáil Minister Rory O'Hanlon serving as Ceann Comhairle of Dáil Éireann from 2002 to 2007, he was guaranteed reelection and therefore the seats were reduced from 5 to 4 in the constituency.

[4] He is the Fine Gael Seanad Spokesperson on Foreign Affairs and Trade.

In 2017, Fine Gael announced that they were planning a bill to allow pubs to open on Good Friday, reversing a 90-year-old ban.

O'Reilly went against his party's view and said that the tradition was "part of our national identity".