Kaplan, who was in charge of Ireland's 19-13 win over England at Lansdowne Road in this year's Six Nations, has been appointed to the potentially-decisive third Test in Auckland on July 9.
The first and second Tests - in Christchurch and Wellington on June 25 and July 2 - will be refereed by Frenchman Joel Jutge and Australian Andrew Cole respectively.
Lions boss Sir Clive Woodward had expressed his hope for the best available officials to be placed in charge, regardless of nationality.
One potential candidate though, New Zealander Paddy O'Brien, has been removed from the International Rugby Board's A panel of referees due to his recent retirement.
Jutge will be assisted in Christchurch by touch judges Cole and Stuart Dickinson, with Kaplan and Dickinson running the lines in Wellington and Dickinson and South African Mark Lawrence handed the task at Eden Park.
Australian Dickinson was involved, as a touch judge, in the sending-off of lock Simon Shaw during England's second Test defeat against New Zealand last summer.
Dickinson will also referee the Lions' pre-tour game against Argentina in Cardiff on May 23.