After an alien's employment based immigration petition (I-140) was approved and before his I-485 petition for adjustment of status is approved, he marries another alien. His spouse may enjoy  immigration benefits based on this marriage as a derivative beneficiary of the approved immigration petition. If his alien spouse is in the U.S. with a valid non-immigration status, the alien spouse may file I-485 petition for adjustment of status. If his alien spouse is outside of the U.S., after he gets the green card, he may petition for the immigration visa for his spouse, and his spouse may get an immigration visa through consular processing.

However, the USCIS has the discretion to examine whether they have a genuine marital relationship. If the USCIS interprets that their marriage was a sham marriage, that is, the sole purpose of the marriage was to circumvent immigration laws, the USCIS may deny the petition.

For more information about Marriage and Immigration, please click the following links:
Introduction
Definitions
Valid Marriage
Unacceptable Marriages in Immigration Law
Existence of Marriage
Marriage Must Not Have Been Entered Into for Immigration Purpose
Immigration Petition for Alien Spouse of a U.S. Citizen of Permanent Resident
Conditional Permanent Residence Status Based on Marriage and Its Removal
Procedures to Remove the Conditions on Permanent Residence
Non-Viable Marriage at I-485 Adjustment of Status
An Alien's Marriage to Another Alien Whose I- 485 Adjustment of Status is Not Approved yet
Marriage in the U.S. Between Parties Both with Non-Immigration Status
A Suspect Marriage and Investigation by USCIS