Someone who's tireless seems to never run out of energy. A tireless student will stay up late to make sure her paper is perfect; a tired student will just go to sleep.
Your tireless efforts might be just what your friend's campaign for student council president needs—you're energetic and enthusiastic, and you'll focus on the campaign unflaggingly. Another way to say tireless is indefatigable. Tireless etymologists have determined that both adjectives date from the 16th century.