Which spacecraft was the first to land on Mars successfully?

Viking 1 was the first spacecraft to land successfully on Mars and continue operating there.

NASA’s Viking 1 lander touched down in Chryse Planitia on 20 July 1976. It transmitted the first clear photographs from the Martian surface and performed experiments to search for signs of microbial life. The mission also included an orbiter that mapped Mars and helped relay communications.

The Soviet Mars 3 lander reached the surface in 1971 and made the first soft landing on Mars, but it stopped transmitting after roughly 20 seconds. Viking 1 therefore holds the commonly cited milestone for the first successful, long-lived Martian landing.

Viking 1 operated on the surface until 1982, far beyond its planned 90-day mission. Its biological experiments produced results that remained difficult to interpret, and no confirmed evidence of Martian life has been established.