| Last updated
The 40-year-old, who is the director of rugby at the Super League outfit, has raised over £1 million for the Motor Neurone Disease Association.
He took on the almighty task after seeing former teammate and close friend Rob Burrow diagnosed with the untreatable nerve condition 12 months ago.
Sinfield had originally set a target of raising £77,777 as the No.7 is synonymous with Burrow but a plethora of donations have seen him smash that total out of the park.
Today, on Monday morning, he completed his final marathon in three hours and 41 minutes. BBC news were on hand to capture the emotional moment he crossed the line.
"It was unbelievable. [I'm] just so happy we got it done," he told BBC.
"After the first day we were all a bit worried we'd bit off a bit more we could chew. The donations and the support just fuelled that last run.
"We were worried we wouldn't get £77,000, let alone what we've done. I can't thank everyone enough.
"We've all been so proud wearing this vest for our good mate Rob Burrow and his family but also the MND community.
"The MND association do so many good things and the sooner we can get some advances for MND, the better for everybody."
A truly incredible achievement.
Chosen for YouChosen for You
Most Read StoriesMost Read