Assemblyman Danielsen received his Associate in Applied Science in Marketing Art and Design from Middlesex County College and his Bachelor of Arts in Visual Arts from Rutgers University. He served in the United States Army Reserve 78th Division TNG (Jersey Lightning) for almost 10 years.

Assemblyman Danielsen is the founder and owner of Network Blade, LLC., a computer consulting service. He has been a volunteer firefighter since 992. From 2000 to 2006 he was a member of the Franklin Township Fire District 1 Board of Fire Commissioners. During his tenure he was integral in creating an inter-local agreement between the township and four fire districts that provided fire fighters during the day. This agreement saved jobs and doubled the level of fire response to the taxpayers at a low cost. In addition, he has served in many volunteer positions within the Township of Franklin, including the Planning Board for 14 years. Assemblyman Danielsen is involved in fundraising for Childhood cancer Research via St. Baldrick's Foundation, Wounded Warrior and the LiveStrong foundations.

Assemblyman Danielsen is the youngest of nine children and was raised by a single parent. He now lives with his wife Christine and their three children, all of whom have attended the Franklin Township public schools.

As a lifelong resident of Franklin Township, Joseph Danielsen, served as Franklin Township Democratic Chairman for six years and Treasurer for two. During those eight years he successfully maintained eight Council seats throughout numerous elections and was instrumental in growing the Committee to record levels. During his tenure he has been a prolific fundraiser throughout Somerset County for Democratic candidates.

For 14 years he served on the Franklin Township Planning Board and served as its vice chair for several of those years. In that role, he consistently supported economic development and helped attract business to Franklin Township while maintaining the local character of historic Franklin Township. He focused on Public Safety and improved the level of safety and response for local volunteers. Assemblyman Danielsen represents the 17th Legislative District, which includes the Middlesex County municipalities of New Brunswick, North Brunswick and Piscataway; and the Somerset County municipalities of Franklin Township and South Bound Brook. He has served as Deputy Whip since 2020. For the 221st Legislative Session he has been appointed as Chair of the Assembly Public Safety & Preparedness Committee, Vice Chair of the Assembly Science, Innovation & Technology Committee and has been appointed as a regular member of the Assembly Labor Committee.