|Rockingham 4 District, New Hampshire House|
| Assumed office|
| Current term ends|
McMahon is the president of McMahon Sales Company Incorporated. He has also been a manufacturing representative and electrical manufacturing representative.
McMahon earned a BA from the University of New Hampshire. He and his wife, Kimberly, have three children; Charles, Brittney, and Shane.
On November 4, 2008, McMahon won election to the New Hampshire House of Representatives from Rockingham County District 4, which sends thirteen representatives to the New Hampshire House of Representatives, by finishing with the third-highest vote total in the election. McMahon received 9,297 votes. The other winning candidates from District 4 were David Bettencourt (R) with 10,390 votes, Mary Griffin (R) with 10,171 votes, Anne Priestley (R) with 9,197 votes, Ronald Belanger (R) with 9,155 votes, Anthony DiFruscia (R) with 9,098 votes, Russell Ingram (R) with 8,367 votes, Robert Elliott (R) with 8,324 votes, Mark Pearson (R) with 8,293 votes, Margaret Crisler (R) with 7,886 votes, Walter Kolodziej (R) with 7,744 votes, David Bates (R) with 7,674 votes, and Carolyn Webber (D) with 7,624 votes. The losing candidates in the race were Marilinda Garcia (R) with 7,472 votes, Jessica Garofalo (D) with 6,544 votes, Doris Flaherty (D) with 6,216 votes, Michael Caruso (D) with 6,204 votes, Carol Schneider (D) with 6,158 votes, Connor O'Brien (D) with 6,089 votes, Camron Iannaflo (D) with 6,041 votes, Fran Brennan (D) with 5,675 votes, Frank Kern (D) with 5,326 votes, Lori Demaine (D) with 5,249 votes, Gerald Capron (D) with 4,423 votes, Henri Azibert (D) with 4,254 votes, and Neelima Gogumalla (D) with 4,160 votes. 
McMahon raised $1,550 for his campaign in 2008. Other candidates in the District 4 race (with data available) raised the following amounts: Griffin ($850), Priestley ($50), DiFruscia ($250), Pearson ($250), Kolodziej ($400), Bates ($2,450), Webber ($875), Garcia ($610), and Iannaflo ($525).
- New Hampshire House of Representatives
- Project Vote Smart profile
- Campaign Contributions: 2008, 2006, 2004, 2002
- Project Vote Smart - Rep. McMahon
- New Hampshire House of Representatives official election results for 2008
- Rockingham District 4 New Hampshire House of Representatives Candidate Funds, 2008