Move confirms rumors that began circulating back in March.
"MIB" marks the third feature film for Clement, who last starred in Jared Hess' "Gentlemen Broncos" and can be seen this summer in Jay Roach's laffer "Dinner for Schmucks" as well as 3D animated pic "Despicable Me."
The New Zealand native joins a cast which already includes MIB vets Will Smith and Tommy Lee Jones. Josh Brolin is also in talks for the Barry Sonenfeld-directed sequel. Brolin will play a younger version of Agent Kay (Jones).
Men in Black III, which is getting the 3D treatment, hits theaters on May 25, 2012.
Production is expected to begin this fall.