The former English international will replace Black Caps bowling coach Shane Bond, who will finish up with team at the end of the Cricket World Cup.
At this stage the 37-year-old has been appointed for only the coming tour of England which will not conflict with his role with the Volts. But if Mascarenhas makes a good job of filling Bond's boots, then he may well be offered an extended contract.
Mascarenhas is in the first year of a two-year contract with Otago and would be lost to the province if that scenario panned out.
''We'll have to play that by ear,'' he said.
''Like I said, it is a great opportunity to be involved in this set up. The Black Caps are just going great guns and hopefully I'll be able to add something to help them go forward.
''All going well and they do offer me something more, then we'll see what happens down the line.
''Until then I'm still with Otago, but this is an unbelievable opportunity for me.''
The big challenge for Mascarenhas will be finding a way to add value to a bowling unit which is operating at the top of its game.
''That is going to be tough. They are going exceptionally well and Bondy has done a great job with the bowling group over the last couple of years. I'm just looking forward to joining the set-up and trying to fill his shoes as best as I can.
''If I can add 5%-10% here and there I'll be very happy.''
New Zealand Cricket head of cricket Lindsay Crocker was delighted to have found someone of Mascarenhas' ability.
''He has worked well with Otago's bowlers and we know he will add value to the team with his vast experience of the English players and conditions.
''He has proved popular in New Zealand, previously as a player and now as a coach and will be a good fit; both in the culture of the side and the skill set required to complement Mike Hesson and his staff.''
Mascarenhas will start his new role on April 15, which is after the Otago season has been completed.
The appointment is a huge vote of confidence in the rookie coach and a nod to his long involvement in county cricket.
''I am newly out of the scene there as a player and I know most of the guys in the current team very well. The new guys I have played a lot with in county cricket and I know all the grounds we are playing at intimately, so those factors will be useful in terms of the scouting and bowling plans.''
''I came to New Zealand with high ambitions for my coaching so to achieve a position like this is hugely satisfying.''
A long-term decision on the role will be made mid-year, with the team's next tour, to Zimbabwe and South Africa, not until the end of July.
