Maradi is located on the National Route 1, the main highway between Niamey and the entire southeast of the country including the cities of Birnin Konni, Zinder, and Diffa, and passing through every administrative region of the country except Agadez. It is also the transportation hub for the region. This makes Maradi as easy and straightforward to travel to as any city in Niger.
By Bush Taxi
Bush taxis are the central means of transportation for most of Niger, and Maradi is the bush taxi hub for the region. If you are traveling within the Maradi region or from Nigeria, this is often your only option; bush taxis arrive and depart several locations within the city for the rest of the region, with costs ranging from 200-1500 francs for within the region.
If you are traveling from other regions of Niger, it is an absolute fact that the buses are cheaper as well as having the fringe benefits of being faster, more comfortable, more reliable, and safer. If you are planning on turning your experiences traveling in Niger into a book and you want the most harrowing stories possible, than definitely try to make this trip by bush taxi. From Niamey, it can take up to 24 hours and is rumored to cost you as much as $30-$60 no, this author has never cared to try it, with lengthy stopovers in several locations along the way, and an old guidebook may have said it best when they described the process as requiring a level of patience on par with Mohandas Gandhi. If you have halfway decent friends, they will certainly save you a seat at the bar for whenever you do get there.
If you are coming from Kano or Katsina, you will probably need to take a bush taxi; no Nigerien bus companies, at least, service Kano or any other city in Nigeria at the time of this writing. Expect it to take eight or ten hours, counting the border crossing citizens of ECOWAS countries don't need papers to cross the border, but westerners will; don't count on your ride being willing to wait for you to go through the formalities, so make good and sure you have an understanding with the driver, or bring your bags with you. Costs and hazards are unknown; among other things, the border has been closed spontaneously and with no warning on at least a couple of occasions, and it is always closed after nightfall.
By plane
Maradi has a working airport, but the country's national airline has long since gone under. Most of the traffic to the airport is government or military during recent joint Nigerien-US military exercises, the airport became quite lively indeed. If you have the contacts, the UN and some other development organizations operate aircraft that call from time to time in Maradi; you can sometimes buy a seat on one of those planes, though this varies from organization to organization and even from manager to manager, not to mention the flight's planned payload, so do not count on it. If you can swing it, you will have the much-envied experience of making the trip in the fastest, most comfortable way possible.
By ship
A seasonal river springs up in late May or early June to the south of the city and flows along until perhaps October, and in some remote places you can find dugout canoes being used as ferries. The author is aware of no regular service along the river in this way, nor of any attempts to market canoe rides to tourists. At any rate, this is not a realistic method to travel to the city.
By car
Maradi is located at the intersection of National Route 1, Niger's principle southern highway, and National Route 9, which runs south from the city through the town of Madaroundfa and into Nigeria, headed for Kano. On National Route 1, a trip by well-maintained car might be about 8 hours from Niamey depending on a number of factors including the time of year, the weather, and the current status of a massive highway maintenance project that was slowly chugging along in the regions of Tahoua and Dossoand 2.5 hours from Zinder. N.R. 1 skirts the city to the north; the turn off is clearly marked in both directions but is very poorly regulated; slow way down and watch for trucks, motorcycles, bicycles, and donkey carts coming from all directions. This turn off will put you on the main street leading to the center of town. National Route 9 is more straightforward; you will arrive in the city from the south and find yourself right on the main street.
Car rental is possible, to this author's knowledge, in Niamey only. It is expensive. Cars can be hired with their drivers in most major cities, including Niamey and Maradi; the rent for the car is somewhat cheaper, though you're still on the hook for the gas as well a the driver's per diem and upkeep. As a general rule, the quality of car you can get will diminish the farther away from the capital you get. It is actually highly recommended to hire a driver along with the car anyway - traffic patterns are distinct in Niger as they are in any foreign country, and the network of police and tax checkpoints can be very difficult to understand. Furthermore, you really don't want to be behind the wheel when you have an accident. Nigerien police officers are typically understanding but highly bureaucratic, so you can count on them to make sure every 't' is crossed and every 'i' is dotted on the reports, no matter how long it takes. Furthermore, the person you had the problem with will recognize you as a foreigner with money, and you can expect that they will show you no mercy in the legal process, no matter how obviously it was their fault.
By train
There is no access to Maradi by train. The closest railhead might be at Kano, Nigeria about 180 km south
By bus
All of Niger's major bus lines serve Maradi with one or two departures and one or two arrivals per day. The price for a ticket is about $20 to Niamey. These buses are reasonably fast, reliable, and punctual at least in their departures from point of origin. They are less uncomfortable, and your ticket will buy you one seat, all your own, so it's the way to travel on a budget. That said, few of these buses have any amenities to speak of; with the rigid seats, the heat, the lack of suspension, and other indignities, the trip can still be brutal, and you can descend from the bus dehydrated, exhausted, and physically in pain on a bad day. Food can be purchased and some deeply troubling bathrooms can be accessed at a half-dozen major stations spaced somewhat regularly along the road; depending on factors like the weather and season, the trip to Niamey can take 8-11 hours. The same network of buses can get you directly to Dosso, Konni, and Zinder, among many smaller towns, and with a one-night stopover you can get to Tahoua, Agadez, Gaya, and Diffa. Many companies also offer international service to destinations including Benin, Togo, and Burkina Faso. Seats are ticketed and they are first come / first serve; don't bet that you can turn up at the station just before the bus leaves and get your ticket. Your ticket also covers baggage; the company might ask you to pay for excess baggage, but normally that's beyond the scope of what a traveler will carry the author never experienced a 'pay-a-fee-so-we-don't-'accidentally'-lose-your-baggage-scam' on his numerous bus trips in Niger, unlike other countries in the region. Do not expect any stowed luggage to be treated gently.
Bus lines with service to Maradi include SNTV the national transport company as well as Aïr Transport that's 'ay-yeer', a name for the northern desert, not 'air' like the sky, Azawad, EHGM, RTV aka "Rimbo Transport", and Sonitrav. Bus companies come and go with some frequency, so check when you get there. In this author's experience, there isn't a whole lot to separate the various companies; their prices and schedules are basically the same. Rimbo RTV has gotten in trouble with the government for having a bad safety record, though every company has accidents from time to time the good news, perversely, for a traveler is that the bus is likely the biggest thing on the road; in most Nigerien bus accidents you're better off on the bus than off it. SNTV has a couple of more modern buses with air conditioning, better suspension, and video players though as those players are often used to play 20-year old kung fu movies and some truly appalling music videos, whether this is a blessing or a curse is open to debate. You are therefore totally sane in choosing your bus based on the convenience of the station. In Maradi, the buses are strung along the main street; EHGM is farther north, SNTV and Azawad are central, near the market, and RTV, Sonitrav, and Aïr are more southerly.