Mantello's secondary career as a director accelerated with his sensitive staging of Jon Robin Baitz's two character drama "Three Hotels" in both NYC (1993) and L.A. (1995). He made his Broadway directing debut with Donald Margulies' black comedy "What's Wrong With This Picture?" (1994), which folded quickly. Only a month earlier, he had successfully helmed Terrence McNally's award-winning play about eight gay men spending summer weekends together, "Love! Valour! Compassion!" off-Broadway. When the production moved to the Great White Way, it received critical praise for its elegiac staging and earned Mantello a Best Director Tony nomination. He has continued to oversee theatrical productions including a 1995 revival of Craig Lucas' "Blue Window".
When the feature adaptation of "Love! Valour! Compassion!" was to be made, Mantello was tapped to direct. A conflict with original cast member Nathan Lane caused a delay in filming. Jason Alexander was selected to replace him, joined by the other original cast members (including John Glover and Stephen Spinella). The finished product premiered at the 1997 Sundance Film festival.