Included as a bonus feature on "The Avengers" Blu-ray, "Item 47" introduced Welliver as S.H.I.E.L.D. Agent Blake, who assigns Agent Sitwell (Maximiliano Hernández) to retrieve a Chitauri gun left behind following the Battle of New York and "neutralize" the couple that found it. In the end, Sitwell instead invites the couple to join the agency.
Welliver will guest star on the Oct. 29 episode, titled "FZZT," in which floating bodies turn up, leading Agent Coulson and his team to hunt down an elusive killer.
News of Welliver's appearance follows Thursday's announcement that ABC has ordered a full season of the series, created by Joss Whedon, Jed Whedon and Maurissa Tancharoen.
Airing Tuesdays at 8 p.m. ET/PT on ABC, "Marvel's Agents of S.H.I.E.L.D." stars Clark Gregg as Agent Phil Coulson, Ming-Na Wen as Agent Melinda May, Brett Dalton as Agent Grant Ward, Chloe Bennet as Skye, Iain De Caestecker as Agent Leo Fitz and Elizabeth Henstridge as Agent Jemma Simmons.