Abe Lincoln could be argued as a 3rd party candidate who won since prior to him it was mainly the whigs and democrats as the two main parties.

Now if you asked what grassroots-led 3rd party candidate overwhelmed the two major parties in a shocker of an election, that obviously never happened.

The last Whig president*, Zachary Taylor, was a political outsider that beat out an experienced politician (familiar?). He was running under the Whig banner because the whigs didn’t have a solution for the issue of slavery- Zachary Taylor was a crude extremely rich celebrity soldier and slave owner who never voted. He was ambiguous on his stance on the future of slavery in America. But the anti slavery wing of the whigs hated this. Taylor ruined the Whig party and it never recovered. Lincoln picked up the anti-slavery whig voters, creating the Republican Party.

The modern day Republicans are only held together with trump and I’m not sure what will happen to their party afterwards. Maybe there’ll be another party “flip” when the Republican Party crumbles, a new more left wing party will rise up as the democrats absorb the former Republican voters, causing the progressive democrats to flee the party. This would be the next success of a “3rd party” candidate. But this won’t happen as long as trump continues to be on the ballot.

*there was Millard Fillmore as the 13th, but this was because Taylor died in office and Fillmore succeeded him as president.