Question Summary:
I am a Sunni Muslim girl from Pakistan. I have a proposal of marriage from a Shia Muslim boy. I want to know ” Is it possible for a Sunni Muslim to marry a Shia Muslim? Are marriages between Sunni and Shia ok? – Is it allowed in Islam? – What implications will it have?

Question Detail:

I am a Sunni Muslim girl from Pakistan. I have a proposal of marriage from a Shia Muslim boy. I want to know " Is it possible for a Sunni Muslim to marry a Shia Muslim?  Are marriages between Sunni and Shia ok? - Is it allowed in Islam? - What implications will it have?

Answer :

In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatuh
 
There are several different types of Shī’ahs, many of them falling out of the boundaries of Islām.  Marriage with such a Shī’ah will be invalid. 
 
Therefore, you should look for a good proposal from a boy belonging to the Ahl al-Sunnah wa al-Jamā’ah (Sunnī Muslims) and not marry a Shī’ah.
 
(فتاوى رحيمية، كتاب النكاح، محرمات: 8/203-205؛ الإشاعت)
And Allah knows best
Wassalaamu `alaykum
Ml. Abrar Mirza,
Student Darul Iftaa
Darul Iftaa, Madrassah In'aamiyyah