It is frustrating to spend hundreds or even thousands of dollars on leather furniture only to have the seams come apart. Over time, or with neglect the leather or the thread deteriorates leaving a gaping hole in the seam. The good news is that you can fix this and the sooner you fix it, the better. If the hole in the seam is small, it should only take you a few minutes to repair.
Depending on whether the thread came loose from the seam or the leather tore, it may be necessary to do some patching first. If the thread just broke and was released from the holes, check the holes in the leather to make sure that they are not stretched or torn. If they are stretched or torn you will need to put a patch over that section before sewing. Find a piece of leather, or even vinyl that matches as closely as possible. Cut a 2-inch strip of leather the length of the hole. Fold the leather in half lengthwise. Glue the new leather over the torn or stretched holes with the old leather in the fold.
After making any gluing repairs, allow the glue to dry for about 24 hours. Look for special leather glue in your local craft store or see if you can purchase a small amount from a furniture repair shop. Since you have added new leather to your couch you will have to punch some new holes. Poke the tip of a very sharp leather needle through the leather or use a leather hole punch.
The thread you use is important when repairing a torn seam in a leather sofa. Do not use regular cotton as it will not hold up to the stress. Instead use a waxed thread that is specially made to use with leather. If you cannot find the waxed thread use a nylon thread. Cut a length of thread that is three times the length of the hole in the seam.
Thread a special upholstery needle with your waxed thread. An upholstery needle is curved and is very helpful when sewing long seams that you cannot manipulate. Double over your thread and knot it at the bottom. To make a knot, wrap the two ends of the thread around your first finger two times. Use your thumb to roll the thread off your finger and pull the knot tightly. Follow the original stitching as closely as you can.
To keep your leather sofa in the best repair possible it is a good idea to condition it at least once a year; twice is better. Purchase special leather furniture conditioner and follow the directions that come with it for application. The conditioner keeps the leather and the thread soft, supple and helps to prevent cracking and tearing.