Is marksman viable for an assassin character? I'm looking at the weapon damage values, and they don't seem like it would be viable.

I think so, a Daedric bow or a bound bow (both easy to get) give plenty of damage and at a safe distance.

Are you kidding me? Of course marksman is viable for an assassin. Taking out your target at a distance is the most perfect way of doing it imo.
But this is just me talking RP. If you′re talking weapon stats, then I′m lost

I know the RP side of it. I'm wondering because of actual ingame weapon statistics. Is it a viable way to kill NPC's?

I can only think of this in terms of RP so I won′t be of much help I′m afraid. Weapon stats never bothers me too much, I only pick whatever I like and go for it. But what it comes down to is your character′s marksman skill I think. To hit with every arrow and with force, that to me sounds more important than a bow′s stats.

Definitely, 50 base damage is plenty (again assuming Deadric/bound bow) With decent levels in strength, agility and marksman, you can kill a Golden Saint in 4 hits.

Maybe marksman does do a bit less damage but it's doing that damage from miles away from the enemy so on average you'll likely manage more damage before you get attacked than with a melee weapon. That's what marksman is all about in games like this really, getting extra damage before melee so it does less damage than melee weapons to balance it a bit. Killing things before melee happens is the realm of higher level characters.

Either way, absolutely anything in this game is a 'viable' way to kill. You just need a more powerful character to benefit from weaker weapons. In the same vein, if you're after single hit kills, nothing is going to work until your character is pretty powerful. An assassin is generally all about killing without getting caught though, at least normally. I don't know what yours is like. There's nothing better for killing without being caught than a marksman weapon from the sneaking stance though.

Unfortunately, Thrown Weapons don't do enough damage to be viable for an Assassin (except for a few specific darts in the one expansion, which I won't go into detail about, here in the General Discussion forum). Bows and Crossbows, however, are VERY effective once your skills improve, especially when combined with a Sneak bonus.

Note: Bows and Crossbows use the damage of the weapon (which can be really significant) + damage of the projectile (trivial in comparison) + strength bonus.
Throwing weapons just use the projectile damage and strength bonus.

Combining marksman with stealth, is extemelly effective in Morrowind. A good stricke while in sneak mode, could end up with your traget prone and seriously injured, supposing the first hit didn't finish him/her.

Envenom all manner of projectiles, and try it out. Arrows from the shadows, bolts from the sky. I'd say a definite "Yes".

Another thing to consider on top of the sneak bonus, is enchantments on your bow. If you're using the Morrowind Code Patch, you can also custom enchant your arrows, for additional lethality. So, decent base damage, plus dual enchantments and a sneak bonus, if that's your inclination. Seems like a pretty sweet deal to me. Then again, I've never tried it personally.

my main character is an assassin type, pretty much the ideal morag tong / house hlaalu guy.
i use marksman and i can confirm the stealth bonus to ranged weapon thing.
also consider that thrown weapons due to their rapid attack rate may "stun-lock" your enemy, forcing them repeatedly into the "ouch"-animation, just like shortswords, but from afar
the better thrown weapons also pack quite a punch, the best regular restocking (farmable) darts beat certain legendary weapons in damage output (so much that BTB adjusted them in his mod).

all in all it's one of my favorite skills, even more so for assassins.