According to The Hollywood Reporter, Gleeson will play the stepfather of Patrick Winslow (Neil Patrick Harris), while Smoove will voice a "naughty" new character.
The pair will join Christina Ricci, whose casting was announced this morning, and returning cast members Patrick Harris, Hank Azaria, Jayma Mays, Sofia Vergara, Anton Yelchin and Alan Cumming.
The first instalment's helmer Raja Gosnell will return to direct.
Glesson stars in Albert Nobbs, which is released tomorrow (April 27) in the UK, and has recently wrapped Robert Redford-directed thriller The Company You Keep.
Ex-SNL writer Smoove has recently appeared in We Bought A Zoo, and has a role in The Dictator, which debuted its opening scene earlier today.
Watch the trailer for The Smurfs below: