If he entered the US unlawfully, under the current immigration laws, he will not be able to legalize his status within the US, even if you marry. He will need to go back to his home country for consular processing but as soon as he departs the US, he will trigger an automatic 10 year bar to reentry, which can only be waived by a showing of extreme hardship to a US citizen spouse, which is fairly difficult to do in most cases. Marriage by itself is not an issue but it will not confer any immigration benefits within the US.
Answered on May 21st, 2012 at 11:54 AM