This is the inland taipan, which possesses the most toxic venom of any snake species on Earth.
The inland taipan and Dubois' sea snake
The snakes with the most toxic venom are not the ones that cause the most fatalities in humans. Actually, each causes very few fatalities compared with other venomous species, because they live in areas that are not heavily populated.
The snake that causes the most deaths in humans is Russell's viper, which lives throughout India, Southeast Asia, and also Southern China and Taiwan. It is commonly found in heavily populated areas and has powerful venom.
The venom of Russell's viper is surpassed in strength by that of some other venomous snakes, and the grand champion, the inland taipan, has venom more than 30 times as powerful. A single bite yields an amount that could kill 100 adult humans.
The Gaboon viper is one of the most dangerous snakes in Africa. The venom glands on this species are enormous, and their bites produce the largest quantity of venom of any venomous snake in the world.
How toxicity of snake venom is measured
The effects of snake venom depend upon the size of the victim. An elephant for example will have a much better chance of surviving a bite than a small rodent.
Because of this fact, the strength of venom is measured according to how much is needed to result in the death of an animal of a particular mass. The venom is measured in milligrams or grams, and the victim is measured in kilograms.
Each venomous snake is given a rating according to their “median lethal dose,” expressed in milligrams or grams of venom per kilogram of the victim. Median lethal dose is the amount required to cause death in 50% of victims.
This formula measures the strength of venom, although snakes can still vary in deadliness due to an additional factor, which is how much venom comes out in a single bite. Some snakes such as king cobras, which are the largest venomous snakes, or Gaboon vipers in Africa, produce huge amounts of venom and therefore even with weaker venom than the snakes discussed below, they are extremely deadly.
It’s been argued that the measurements, which are done using mice, may not apply as accurately as many scientists think to humans due to differences between mice and humans. However, no one is going to test venom out on humans, so the scale that exists based on mice is what is used.
The coloration of the inland taipan may change to yellowish during the summer months. 
The inland taipan of Australia
Australia is the venomous snake capital of the world. The top seven most venomous snakes live in or near (in the case of sea snakes) Australia, and eight of the top ten are found within, or along the coasts of, Australia.
There are multiple ways venom is administered to mice for the median lethal dose scale listed above, and the method I’m using (since numbers using it are the most available) is called subcutaneous injection LD50. The rating on this scale for the inland taipan is 0.025 mg/kg.
The Russell’s viper mentioned in the introduction has a rating of 0.75 mg/kg, which means 30 times as much is needed as the inland taipan to have the same result. The most venomous rattlesnake species, a snake I'm familiar with here in California, has a rating of 0.6 mg/kg, meaning the inland taipan’s venom is 24 times as powerful.
Inland taipans rarely bite humans, because they live only in remote areas of Australia’s semi-arid interior and are also quite shy. However, if they are provoked or otherwise feel threatened, they strike very quickly and accurately, and may strike multiple times. Anyone bitten may not live more than 30 to 45 minutes.
Anti-venom exists for another taipan species in Australia, the coastal taipan, a species which in fourth place of all venomous snakes. This anti-venom helps with those bitten by inland taipans but may not be available nearby for anyone in the remote areas where this species lives.
They reach six to eight feet (1.8 to 2.4 meters) in length and can be a variety of colors – tan, yellowish, greenish, or dark brown, almost black. They change color according to the seasons, being lighter during the summer and darker during the winter. They specialize in hunting and eating small mammals.
Sea snakes are fully adapted to living in the Earth's oceans.
Dubois' sea snake of the Indian and Western Pacific Oceans
Although found along the coasts of Australia, our second place winner for most venomous snake on Earth is also found through parts of the Indian Ocean, and in seas to the north of Australia, near New Guinea, and east toward New Caledonia. Their venom rating on the scale discussed above is 0.044 mg/kg, meaning slightly more than half as powerful as that of the inland taipan.
Sea snakes are fully adapted to living in the oceans, and all but a few cannot move on land at all. There are at least 62 species, and all are venomous. They all live in a range similar to Dubois’ sea snake, meaning throughout the Indian Ocean, near Australia and Indonesia, and in the western Pacific Ocean.
They have paddle-like tails, and most can partially breathe through their skin. Most are reluctant to bite humans, although fatalities have occurred at times. Four of the top ten most venomous snakes are sea snakes, and Dubois’ sea snake is the most venomous of them all.
Dubois' sea snake typically reaches 3 to 4.5 feet (about 1 to 1.5 meters) in length, and coloration and patterns on their scales have a huge amount of variation. As with all but a few sea snake species, they give birth to live young rather than laying eggs. They eat fish and eels.