Roy Baumeister answers
Meaningful lives tend to be happy, but there is no guarantee. Some ways to make life meaningful do not bring happiness. Terrorists, missionaries, and various international development workers may derive immense meaning from their work but probably fewer joys and pleasures than many other lives.
Still, the pursuit of happiness that ignores meaning is likely to fail. Happiness without meaning tends to focus on short-term and even selfish pleasures. Deeper sorts of satisfaction require integrating past, present, and future, and for that you need meaning.
Roy Baumeister is a professor of social psychology at Florida State University.