McDowell was an unsuccessful candidate at the 1989 general election in the Dublin North–Central constituency, but at the 1992 general election he was returned to the 27th Dáil, topping the poll with 23% of the first-preference votes. He was re-elected at the 1997 general election with a much reduced share of the vote, but lost his seat at the 2002 general election to the independent candidate Finian McGrath.
After the loss of his seat in Dáil Éireann, McDowell was elected to the 22nd Seanad by the Industrial and Commercial Panel, where he was Labour's Seanad spokesperson on Finance, Transport, Enterprise, Trade and Employment. At the 2007 general election, he stood again in the Dublin North–Central constituency, but did not regain his seat. He did not contest the subsequent elections to the 23rd Seanad.
- "Mr. Derek McDowell". Oireachtas Members Database. Retrieved 8 January 2008.
- "Derek McDowell". ElectionsIreland.org. Retrieved 9 January 2008.
- "General election, 17 May 2002: Dublin North–Central". ElectionsIreland.org. Retrieved 9 January 2008.