Can I Extend exFAT Partition on Hard Drive? And How?

I have an external hard drive with 120 GB of unallocated space on it. When I try to extend my main partition, the option to extend volume is greyed out in Disk Management. Is there any way to extend the partition to make it all one partition?

According to what you said, the likelihood is that the unallocated space is not behind the exFAT partition, which leads to the "cannot extend volume" problem. Another main reason is that your partition is not NTFS, so the Windows program won't let you resize it. In this case, you need to rely on professional partition-extending software to extend or shrink partitions with adjacent/non-adjacent. 

EaseUS Partition Master has a good reputation, and it's an expert in partition management. It can offer a once-for-all solution to fix the "Extend volume greyed out" problem by using the "Resize/Move" feature to add non-adjacent unallocated space on the target partition. In addition, this software can also allocate space from other partitions when there is no free space on your hard drive.

Note: Although EaseUS Partition Master is safe and extending the partition will not delete your data, you must prepare a data backup for incorrect operations.

After the above action, the unallocated space may be successfully added to the existing partition. However, if your hard drive is running out of space and has no free space, you will discover the solid solutions in the following article:

Related Article: Expand the Partition Without Unallocated Space