WordNet records no synonym and no antonym for last laugh. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
ultimate success achieved after a near failure (inspired by the saying `he laughs best who laughs last')
“we had the last laugh after the votes were counted”
Synonyms, antonyms and the broader and narrower relations for last laugh come from Princeton University’s WordNet. Full sources and licences.