Life's Too Short is a fictional account of the life of actor Warwick Davis.
Neeson and Bonham Carter have now both agreed to appear in the comedy, The Sun reports.
Johnny Depp, Cat Deeley and Sophie Ellis Bextor have already signed up for cameos alongside Les Dennis, Shaun Williamson, Sting and Steve Carell.
Gervais recently denied claims of "dwarf cruelty" on the set of Life's Too Short. Meanwhile, Davis has described his role on the show as a "dream come true".
Life's Too Short will air on BBC Two later this year in the UK. HBO has picked up the US rights to the series.
Watch a preview for Life's Too Short below: