Marry without dating
For clarity's sake, the Arranged Marriage trope will deal only with more binding, traditional types of unions.See also Parental Marriage Veto, You Have Waited Long Enough, Old Man Marrying a Child, Homosocial Heterosexuality, Royal Inbreeding, and Marriage Before Romance.Most people don't really want to marry a total stranger (much less have sex with them), and if that total stranger turns out to be a complete rogue and a cad, it may be necessary for the heroes to spring into action and rescue the hapless member of their group who is being forced to walk down the aisle.(Of course, being Big Damn Heroes, they'll have to do so in the most overblown and dramatic way possible.) Sometimes, the person in the arranged marriage takes matters into their own hands and becomes a Runaway Fianc.
Conversely, an Arranged Marriage can be used to lock the hero and heroine together so that their disputes can not end with one of them washing their hands of the other.
If the people doing the "arranging" in the marriage aren't the parents, that's a Bureaucratically Arranged Marriage.
Often involves Prince Charmless and Rebellious Princess.
A Shotgun Wedding is a short-notice forced marriage.
If someone agrees to an Arranged Marriage but loves someone else, Courtly Love may be involved.