In order to become a government consultant, it is necessary to be an expert in a certain field. Government consultants are hired in various departments to perform tasks and to undertake projects, so there is no particular requirement for a certain type of knowledge. You could become a government consultant doing scientific research or working on a budget, as the needs are highly different depending on your area of expertise and the government's needs at the time. Education is generally required to become knowledgeable enough in a field to provide consultations on it. Many times, it is necessary to have good problem solving skills to become a government consultant because you are being hired to help fix something that is not working correctly.
Consultants generally need to be educated in the field that they are in. In certain cases, a government will hire a consultant who only has a bachelor's degree, but in many cases, a master's or doctoral degree is required. When being hired with only a bachelor's degree, you would generally begin in a more entry-level position assisting others with tasks and projects. The more education you have in an area will determine the level of supervision that you need to do your job well.
Experience is almost always necessary to become a government consultant. Since you are being hired to help fix things that haven't gone correctly, you need to have done similar work in the past. You can get experience by working in a private field before attempting to become a government consultant, or by working your way up from an entry-level position at any organization. During college, it is a good idea to participate in an internship program and research to gain the experience needed to initially get a job after graduation.
Once you have the education and experience, you can decide how you would like to enter into the field of consulting. Some people work for themselves while others work for large agencies that employ many consultants, so this is something to consider. If you join a large consulting firm, you will have less control over the projects that you undertake, as your employer will help decide this for you. On the other side, however, is the difficulty in getting contracts as an independent consultant. The better you are at problem-solving, the easier it will be for you to work, whether working independently or for an organization.