Guy Nadeau's interest in public service began during his years at Assumption College, where he earned a degree in political science in 1979. He then worked for the Census Bureau and as a volunteer for Senator Edmund Muskie in 1980. In 1983, Guy became clerk of the Maine Legislature's Committee on Governmental Affairs and also the Taxation Committee. In 1984, he was elected State Representative from District 16, which encompassed most of Saco, and represented the area until term limits precluded him from seeking re-election in 1996. During his tenure in the legislature, Nadeau served on the Taxation Committee and the Committee for State Government, which helped to establish Maine's technical college system. He was a House of Representatives chair of the Ways and Means Committee from 1987 to 1992 and chair of the Committee on Veterans and Legal Affairs form 1993 to 1996. During his years in legislature, Nadeau was also active in many community organizations. He was a founding member of the Saco Community Activities Committee, has been a corporator of Sweetser's Children Services. He has served on the board of director of Southern Maine Parents Awareness and the anti-drug organization STANDD-UP. He has also volunteered countless hours helping to found CYO at Most Holy Trinity Church, serving as a member of the TA Athletic Boosters during the 1980s, volunteering on the TA annual fund and helping to plan his class reunions.