How can I support my partner through work related depression?

It sounds like your partner is in a very difficult situation, and is actually doing everything he can to improve it. It also sounds like you are doing all that you can to support and comfort him in his struggles. Sometimes the most difficult thing to accept is that, even when we are doing all that we can, things will not improve quickly. It's also very sad that you are not able to celebrate and look forward to the arrival of your child because of how tough things are at the moment.
Some of the ways you may think about helping your partner and yourself to get through this difficult time may be:-
* Actively cultivate acceptance. Accept that each of you are doing the best that you can, and don't give yourselves a hard time for what you are unable to change at the moment.
* Redirect your focus on to what is good right now, and celebrate those things. Taking time to notice and express gratitude for what is going well can be a powerful mood-changer.
* Challenge negative self-talk. Depression can be contagious! That is, it can be difficult not to become ‘infected’ with the sense of hopelessness that things will ever be better. When you notice you have ‘bought in’ to unhelpful thinking, actively challenge it within yourself. For example - if you notice the thought “ Nothing I do or say makes a difference”, you may try thinking about the times something you've said or done has helped your partner, even for a little while, or in a small way.
* Find the positives in a way that makes sense to you both about what you are going though at the moment. An example of this may be “Things are really tough right now, but we are good at actively seeking help and not giving up no matter what.”
* Get some additional support for yourself. It's hard work supporting a loved one with depression. Supportive counselling for you may help you ‘refill the tank’ so you do not become too depleted in your role caring for your partner, and provide a space just for you to talk about your own feelings and struggles.

These are all tips for getting through a difficult time. It's like accepting that you're both running a marathon rather than a sprint right now, and need strategies for pacing yourselves so you can both get to the end. 
All the best

Things are tough. Tough times are can be used two ways let it consume us or use it as the motivation/reason to change what you are doing. Losing the grip of depression does not happen overnight and takes time. There is no silver bullet - sometimes we need to have medication, eat healthly, exercise, good sleep, self care, counselling and routine all happening at once for depression to lose its influence. If you are feeling depressed at times then you need to look after yourself and once you start doing that you will feel stronger and better able to support your husband. Perhaps both of you going to counselling together could be an option witht he focus being to support each other not on your husband. Take Care. Congrats on your pregnacy.

I really feel for you as I have experienced something similar in a past work role. Maybe your partner can seek external advice and help form a union representative or other external organisation.

When anyone comes to me with any dificult issue such as yours I suggest to the person to put it down on paper. Make a list of what is happening, who is involved and a list potential solutions. This gets it out of your head so you can both look at the whole situation objectively.

Mind Mapping is also a very powerful tool, google it and try it, you will be surprised at the new perspective you gain. Doing this alone seems to calm the mind which will help a person think clearly. 

Maybe suggest to your partner that he try Life Coaching to compliment counselling. It tackles the issue in a different way.

Remember to look after yourself especially since you are pregnant. You may consider counselling for yourself as you may learn some coping skills that will help you both.

It sounds like you both need support. Encourage your partner to distract himself with mentally stimulating activities such as puzzles, word finds or any other engaging hobby. Taking time out for hobbies of interest and those that give him confidence can help to reduce depressive symptoms. He could join a support group for depression sufferers. Also, perhaps he could find aspects of his job that he enjoys, or he may want to talk or debrief with a friend. Exercise and social contact is also important. You also need to find interesting and enjoyable activities you can do with your partner. Good luck.

There are some really good suggestions above. Also I would add that it is really important for you to get some counselling for yourself. The see-saw of being effected by his moods and depression is something that you will be able to get support in counselling for. You can learn how to manage your own emotions better even while he is struggling and learn how to avoid the temptaion to try and rescue him which will only leave you both feeling more disempowered. It is hard but a journey for your own self discovery as well. All the best.