Adult marrying secretly with just Imam and witnesses
Question
 Can an adult over 25 years old virgin male or female get married secretly with just the imam and witnesses?
Answer
Marriage is a sacred institution that brings with it honor, respect and dignity, and for that reason Islam has given many guidelines that are connected to proposal, acceptance, guardians, witnesses, Mahr etc. etc. The Prophet (SAS) has also emphasized upon us that one should announce his marriage. This is done so that people would know that a person has married, and they will refrain from falsely accusing a person when he/she is seen with the opposite sex. If it is not known that one is married, then the character and honor of a person can be damaged, since he/she can be accused of having a haram relationship with another person. Announcing a marriage therefore protects a person, while keeping it a secret, damages the character.
The Prophet (SAS) also told us that the guardian of the girl must give consent for the marriage. This is also given in order to prevent a girl from making wrong decisions about the person she wants to marry.
Many scholars have held the position that even in the case of an adult female, she must still get the consent of her father/guardian for marriage. Along with this, others have held on to the other position that announcement of the marriage is necessary.
Both of these conditions which are evident from the above traditions make it abundantly clear that Islam does not favour secret marriages. This brings nothing except damage to the character of a Muslim man/woman.
Howbeit, some scholars have stated that the minimum requirement for a valid marriage in Islam is the proposal and acceptance, the Mahr, and two witnesses. These scholars have stated that once these are in place then the marriage is valid.
Based on this, it means that if the Imam or another person does the marriage of two adult Muslims (male and female) in the presence of two male witnesses, then the marriage will be valid. (as you have asked).
As I have mentioned before, this is the minimum requirement that has been given by some scholars for the validity of a Muslim marriage. This, in no way indicates that secret marriages are encouraged, nor is this the way to contract a marriage. The scholars have highlighted these as the ‘least amount’ that is needed for a marriage, without which, a marriage will not be valid.
So, based on what you have asked, the marriage will be valid when there is the proposal and acceptance, the Mahr and the two male Muslim witnesses.
And Allah knows best.
Mufti Waseem Khan