Steinfath, 24, arrived in the Norwegian port city of Kristiansand after paddling 137 kilometres from Denmark while standing on his surfboard.
The stand up paddleboarder had left Hirtshals in Denmark just under 19 hours earlier.
“I really wanted to give up on the way. It was so tough and my body is completely empty right now. But I did it and it feels fantastic,” Steinfath said.
Stand up paddle surfing is an offshoot of surfing in which riders stand on their boards and use a paddle to propel themselves through the water, instead of sitting until a wave comes.
Steinfath completed the journey between the two Scandinavian countries just before 8pm on Sunday.
“The last four hours were an extreme struggle. I was paddling in a side wind and with a lot of current, but my brother was shouting from a support boat that I was going to do it, which helped me not to give up,” the Dane said.
The 24-year-old, who is a four-time world champion in the discipline, said preparations for the long trip had been difficult.
“Weather conditions are impossible to know in advance. Skagerrak is in charge and I just have to paddle,” he said.
A similar attempt to make the crossing in 2017 was aborted by Steinfath 12 kilometres short of the finishing line due to adverse weather.
“I prepared differently this time. For the last month I've been getting up at 3am to prepare my body for paddling in the dark and cold,” he said.
A dinghy with two lifeguards on board and a 12-person support boat were behind the Danish surfer as he made the crossing.
But no assistance, other than handing over food rations and moral support, was needed as the crossing was successfully completed.
At around 6pm on Sunday, press officer Ole Svarrer had warned that Steinfath was experiencing difficulties.
But the Danish surfer came through to complete the feat and arrive in Norway.