Mabius will play Senator Peter Caldwell on the ABC drama's second season, according to The Hollywood Reporter.
A member of a powerful political clan, Caldwell will turn to Olivia Pope (Kerry Washington) for advice in forthcoming episode 'Boom Goes the Dynamite' - to air on February 21.
Mabius is best known for playing Daniel Meade on ABC series Ugly Betty between 2006 and 2010 and has since appeared on TNT's Franklin & Bash, USA's Political Animals and short-lived BBC sci-fi drama Outcasts.
Last month, he also signed up for a guest stint on CBS cop drama Blue Bloods opposite Tom Selleck and Donnie Wahlberg.
Scandal earlier this week signed up former House star Lisa Edelstein for a guest appearance - the actress will play a new client of Olivia Pope & Associates.
The show airs on Thursday nights on ABC in the US, with season two expected to screen on More4 in the UK later this year.
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Watch a promo for the next US episode of Scandal below: