The narrative of Mars is set in the year 2033, following the maiden voyage of the spacecraft Daedalus on a mission to establish the first human colony on the Red Planet. The story is presented as a unique hybrid, blending a scripted drama about the mission with documentary sequences featuring contemporary scientists, engineers, and innovators like Elon Musk and Neil deGrasse Tyson, who discuss the real-world challenges of interplanetary travel. The fictional crew is an international team of six highly trained astronauts: American mission commander Ben Sawyer, Korean American pilot Hana Seung, Spanish hydrologist Javier Delgado, French physician Amelie Durand, Nigerian mechanical engineer Robert Foucault, and Russian exobiologist Marta Kamen. Back on Earth, their progress is monitored by a control team including Hana's twin sister, Joon Seung, who serves as a capsule communicator.

The story begins with a harrowing descent to the Martian surface, during which the Daedalus suffers a malfunction, landing far off-course and severely injuring Commander Sawyer. The crew must traverse the harsh, unforgiving terrain to reach their intended base camp. Sawyer eventually succumbs to his injuries, forcing Hana Seung to assume command. The team struggles to find a permanent, safe shelter, which hinges on locating a source of water. After a series of life-threatening challenges, they discover a lava tube that provides natural radiation shielding, allowing them to establish a settlement named Olympus Town. The first season spans several years, covering the arrival of a second crew. A major crisis occurs when a prolonged, planet-wide dust storm traps the inhabitants in their habitat, leading to psychological breakdowns; one botanist, driven mad by the loss of his crops and the isolation, opens an airlock, killing himself and several others. Just as the mission on Earth faces a vote to end the program, the storm subsides, and Marta Kamen discovers microbial life on Mars, ensuring the colony’s future.

The second season jumps forward to the year 2042. Olympus Town is now a thriving, fully-fledged colony, but the International Mars Science Foundation (IMSF) lacks the funds to continue its mission alone. This financial gap opens the door to the private sector, specifically the for-profit corporation Lukrum Industries, which sends a team of miners to extract water and other resources. This creates a central conflict between the original mission-driven scientists and the new corporate arrivals, who operate under fewer restrictions. Hana Seung remains the commander of Olympus Town, while her sister Joon finally joins her on Mars. The narrative explores the tensions of this co-existence, with Lukrum’s aggressive mining causing a series of disasters. A solar flare knocks out power, stranding Marta outside during a critical mission. A mysterious and deadly illness, potentially linked to newly discovered Martian microbes, sweeps through both colonies. The first Martian baby is born prematurely, and a romantic relationship briefly blossoms between Hana and Robert Foucault before he defects to work for Lukrum. In the season's climax, Lukrum’s push for resources leads to a catastrophic underground explosion that triggers a powerful marsquake, severely damaging both settlements and resulting in multiple deaths. The survivors work to stabilize the situation, and the series concludes three years later in 2045, when the colonists observe the first cloud in the Martian sky, offering tangible evidence that their efforts to terraform the planet are beginning to succeed.