The 50-year-old "LA Law" actor will be back for multiple episodes as Melinda May's (Ming-Na Wen) ex-husband, after last appearing in the two-part season two finale, reported Variety.
The actor will reprise the role of Andrew Garner, who first appeared in the episode "One of Us".
However, Underwood's storyline and the status of his relationship with Agent May is being kept under wraps.
The upcoming season three will introduce characters based on Marvel's "Secret Warriors" comics.
"Agents of SHIELD" is set to return to ABC on September 29.