The big event will take place at the Royal Palace church in Stockholm and the date was decided upon by the couple after discussions with King Carl XVI Gustaf and Queen Silvia, the newspaper Expressen said Sunday.
Followers of Swedish royalty told the TT news agency the venue was much smaller than the church where Princess Victoria tied the knot, which means the wedding ceremony will be on the intimate side.
Madeleine and London-born O'Neill have been an item for about two years and it was revealed earlier this year the couple had been living together in O'Neill's New York apartment since fall 2011.
The Local.se said the princess has been working with a child-advocacy non-profit while O'Neill is a partner with Noster Capital.
2014: The Year in Music [PHOTOS]