Answered by: Maulana Maruf Ahmed
Hi Sir, My question is I married a girl who changed a religion from Sikhism to Islam very next day of her conversion. on 14 Dec. .2012 but she was already married in India and not divorced. Is my marriage with her without a divorce from her first husband after conversion to Islam valid and recognisable? Was Iddah period necessary for her before her marriage with me? Kindly guide me because mosques don’t affirm my marriage taking a position that pre Islamic marriages are sound and valid unless dissolved through legal channel. Conversion to does not invalidate them. kindly give me true interpretation.
If a non-Muslim woman accepts Islam whilst being married, and her husband does not accept Islam, her marriage with him breaks immediately. She is required to observe the ‘iddah (3 menstrual cycles). If her husband does not accept Islam within this period, she may remarry. This is irrespective of whether her previous husband has acknowledged that the marriage has been terminated or he hasn’t legally divorced her. 
Only Allah knows best.
Written by Maulana Maruf Ahmed
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Ibn Abideen, Radd al-Muhtar: vol. 3 pg. 191, Dar al-Fikr, Beirut)
This answer was collected from DarulIftaBirmingham.co.uk, which is run under the supervision of Mufti Mohammed Tosir Miah from the United Kingdom.