I don't think they must match, but could you post a picture?

I think that a leather sofa would work if:
* you looked for one with a similar color value as your velvet. By this I mean, a similar darkness (not hue/color) to both. By doing this, the eye will travel easier from one to the other.
* keep the sofa styles similar (no skirt; similar lines, size)
* Do you have throw pillows that match the velvet sofa? If so, I'd move them to the new leather one to tie the two sofas together more. If not, you might consider making four pillows in a coordinating fabric to use on both.
* Try to add leather somewhere else in the room if you can.

I snapped a quick photo - please excuse the yellow towels - I was using them to slide the sofa around while playing with the arrangement. The fabric is actually much darker and richer looking in real life. The flash seems to have washed this out a bit.

I'm thinking a brown leather might work if the shape is similar but would another fabric sofa be okay or best be avoided?

What about something in a very similar style, but different color. You could coordinate them with a throw across the back and accent pillows.
{{!gwi}}

Here is a link that might be useful: Claremont Sofa