In heavy saucepan, soak wild rice in boiling water for 30 minutes.
Drain; rinse thoroughly.
In large skillet or Dutch oven, combine drained wild rice, brown rice, onion, carrots, celery, chicken broth, thyme, marjoram, salt, and black pepper. Bring to a boil over high heat.
Reduce heat to low and simmer, covered, until rice is tender and liquid is absorbed, 50 to 60 minutes.