Some of the victims had been accused of murdering a police chief, but were acquitted after a trial.
Angry about the verdict, a mob of racist vigilantes in the city attacked and publicly hanged them.
Mayor LaToya Cantrell is due to apologise for the killing - believed to be the largest recorded lynching in US history - on 12 April.
She will issue the apology at an Italian-American cultural centre in the city, a spokesman told the Associated Press news agency.
What happened in 1891?
Commissioner David Hennessy - a police chief in New Orleans - was ambushed and killed by four men near his home in October 1890. It is thought that with his dying words, he blamed the attack on Italian immigrants.
A large Italian community had moved to the city after the civil war and the abolition of slavery, to take up jobs that had formerly been done by slaves.
Following Hennessy's death, officials rounded up Italian immigrants - according to some reports, they apprehended thousands.
Nine men ended up going to trial in February and March the following year. Six of these men were acquitted, and the other three cases ended in a hung jury.
Then on 14 March, a large mob stormed the jail where the men were being held, dragged them out and killed them.