Nelsen is a native of West Palm Beach, Florida. He moved to New York City with his family at the age of 13. Eric married actress Sainty Reid (now Nelsen) in Fort Worth, Texas on November 29, 2013, and his wife gave birth to their daughter Molly Morgan Nelsen on October 1, 2019, in Los Angeles, California.
He is best known for his work as an actor in Hulu's revival of All My Children playing AJ Chandler and most recently, his recurring role in season 4 of Showtime's hit drama The Affair. On stage, Nelsen portrayed Brett Sampson in the original Broadway production of 13 The Musical and starred with Gretchen Mol in The Good Mother, produced by The New Group. He has appeared in over 30 television series, including The Blacklist, Girls, The Following, NCIS, Blue Blood, and iCarly. Nelsen has also appeared in the Universal Pictures film, A Walk Among the Tombstones opposite Academy Award nominee, Liam Neeson, and Coming Through the Rye opposite Academy Award winner, Chris Cooper.
In 2018, Nelsen most recently won a Daytime Emmy Award for Outstanding Supporting Actor in a Digital Daytime Drama Series for his work on the Amazon web series The Bay. As a producer, Nelsen has won three Daytime Emmys for his work producing The Bay and holds the world record for youngest Emmy Award-winning producer in television history. He also produced the indie feature, Wakefield starring Bryan Cranston and Jennifer Garner.