Does RCV respect the principle of “one person, one vote”?

Yes. Under Ranked Choice Voting, every voter gets exactly one vote, and each vote is treated equally. Like a runoff election, a vote under RCV initially counts for the voter's first choice, and if that candidate is eliminated, for the voter's next choice still in the running. In fact, the academic name for RCV is the “single transferable vote” — emphasis on single — and the value of that single vote does not change at any stage in the process.

Every court to decide the issue has agreed that Ranked Choice Voting gives each vote equal weight. The Massachusetts Supreme Judicial Court has ruled on the question twice in fact. First in 1941, they wrote in Moore vs Election Commissioners of Cambridge:

“Each duly qualified voter has the same right to mark and cast his ballot as every other duly qualified voter. Each duly qualified voter has the same right as any other such voter to one and only one effective vote for a candidate.”

Then again in 1996, in response to a procedural question about filling a vacancy in McSweeney vs City of Cambridge, the court reaffirmed the broader constitutional claim of Moore:

“[A] preferential scheme, far from seeking to infringe on each citizen's equal franchise, ... seeks more accurately to reflect voter sentiment ... This purpose is not a derogation from the principle of equality but an attempt to reflect it with more exquisite accuracy.”

At the federal level, the Ninth Circuit Court of Appeals concurred in 2011, writing unanimously in Dudum v. Arntz:

“In fact, the option to rank multiple preferences is not the same as providing additional votes, or more heavily-weighted votes, relative to other votes cast. Each ballot is counted as no more than one vote at each tabulation step, ... and each vote attributed to a candidate, whether a first-, second- or third-rank choice, is afforded the same mathematical weight in the election.”

Misconceptions about unequal treatment under RCV may stem from examples of voters who do not rank all the candidates. For instance, a voter may rank only their first choice, omitting the other candidates from the ballot because they have no preference between them. Some may incorrectly claim that this voter is being discriminated against. To the contrary, this voter is choosing to not express a preference between the remaining candidates — to abstain — and therefore has the same opportunity as those who choose to mark a preference. This is equivalent to a voter who chooses not to vote in a runoff election because their favorite candidate didn’t make it past the first round. The opportunity to vote for a candidate in the final round is open to all.

After the historic use of Ranked Choice Voting in Maine in 2018, the issue was reviewed yet again by a federal court. In Baber v Dunlap, the US District Court of Maine concluded:

“‘One person, one vote’ does not stand in opposition to ranked balloting.”

And no court has ever found otherwise.