It is not required to have a shaykh to perform an Islamic marriage ('aqd, nikah). 

However, in most cultures, a religious, spiritual, or community leader customarily performs a marriage. This lends a certain sanctity to it, and also gives it a social and communal recognition and situates it into the tapestry of the community, moving it from merely a private relationship to a communal one.

It also adds an extra security or safety network in case there are, later, questions or difficulties about the marriage. 

In my observation, Islamic marriages which are conducted privately by the bride and groom, or informally (say, by the bride and groom's friend) and which are done outside of a social structure often do not seem to have the longevity of marriages which are done by a third party who is recognized by the community.  Or, sometimes there is something about the situation that is not quite right. 

Exceptions  apply of course. This is not a matter of halal or haram, merely an observation.

If one is planning to get married without a shaykh or religious leader involved, a good question is why - is there a genuine reason why this is being done, and is all well? Or is there something not quite right about the situation that they don't want someone to know about, that might later resurface and cause problems in the marriage? 

Just some thoughts. Wishing everyone the best in their marriage life!