In the original game, there would occasionally be a vote to choose the new marshall, two candidates will be listed and every other lord of that faction will get one vote toward who they want. If you are a vassal, you may cast one vote as well. The candidate you vote for will like you more (+2) and the one you didn't vote for will like you less (-2), regardless of which one wins.
If your Renown is high enough, you may be given the option to be a candidate, which you may refuse if you want. If you are a candidate, the voting will progress in much the same way, except you don't get to cast any votes yourself. If you win the vote, you become the new marshall and your opponent that lost will like you less (-3).
The marshall doesn't always need to get in by a vote, sometimes the monarch will just quietly appoint a new one.
Your standing with the given faction or your friendship with particular lords seems to be of secondary importance. If your Renown is low, you may have a hard time becoming Marshall even if you have your standing with the given faction maxed. On the other hand, if you start off the game as a factionless bandit-hunter, rack up 1500+ Renown, then join a faction and there happens to be a Marshall election, you are almost guaranteed to get the title, even if you've never spoken to any of the lords before.
If you are factionless and then accept a faction leader's offer of servitude, Marshall elections very often happen soon after you place your vows (within a few game days or even hours).
Serving the marshallEdit
If you are not the marshall, you may occasionally receive orders from them when they start a new military campaign. These orders are Quests, you do not have to do them, but if you fail, you will lose reputation with the marshall.
The first order you will get is to report to the marshall with a minimum amount of soldiers. Typically the number of troops you will need will be much lower than you would normally have except possibly in very early game. However, what types of soldiers you have doesn't matter, fresh recruits will work just as well as top tier knights or infantry.
Once you have joined up with the marshall, you will usually be told to follow them for a while. During this time, you need to stay within sight of them. If you wander too far away, you will be warned to return. If you do not get back quickly, you will fail the quest and irritate the marshall.
The marshall may give you some other missions, these will supersede the instructions to follow him until you have completed them. Once the marshall's army has besieged an enemy fortification, the campaign will generally end and you can go back to your own business.
Being the marshallEdit
Being the marshall gives you the power to give orders and organize military campaigns. You will also have full authority over your allies in battle, so you may instruct their troops just as you would your own.
To give orders to your fellow lords (including the monarch), just speak with them and select "I have a new task for you." A list of orders will then be shown.
If you wish to head a military campaign, talk to any vassal and tell them "I want to start a new campaign. Let us assemble the army here." This will send out a message to all the vassals with instruction to meet you at that location.
To cancel orders, tell the lord "I won't need you for some time. You are free to do as you like."
You can also use your heroes to start or end a campaign, given you have heroes with you. Just talk to any of them, the option to start or end a campaign is the first one on the list.
In Warband, controversy can make your time as marshall very brief. Every time anything bad happens to your faction, your controversy can increase quite rapidly. The larger your faction, the more difficult it is to maintain order.
Once your controversy starts nearing 100, your monarch will want to replace you.
It is important to note that vassals will not always obey you. When given a direct order, if they are preoccupied with something else already (like heading to their castle), they may tell you they are too busy.
If they are not busy, they must listen to you, but may only do so for a limited length of time. This means that if you instruct a fellow lord to follow you and then besiege a castle, he may wander off before you even finish constructing the siege equipment. All lords, even ones that like you, will also be tempted to chase passing caravans or enemy farmers as well (this is less likely in Warband).
If you are not playing with realistic saving, you should save before starting the siege so that if all your allies run off, you can restore and try again. It is advisable to tell all your comrades to follow you again just before starting the siege, this will decrease the likelihood of them losing interest before the actual battle begins.
Calling together a military campaign can be even more frustrating, as it can take a long time for everyone to come together and the lords may ignore your summons completely too. If you only have one objective in mind, it may be faster to just manually give three or four lords direct orders to follow you rather than attempt starting a campaign.