The former Xena: Warrior Princess star was among a group of seven campaigners who climbed aboard the vessel, which is docked in Taranaki, New Zealand, on Friday to protest against oil drilling in the Arctic.
They have vowed not to leave until the Noble Discoverer's mission is called off.
Police were called to the scene and five officers boarded the boat, but they decided against removing the protesters amid safety fears, according to Stuff.co.nz.
One man, who was not on the ship, was arrested at the entrance to the port, while Lawless and the other campaigners are also facing detention, but Inspector Blair Telford has confirmed cops currently have no plans to remove them from the vessel.
He says, "Although the protesters are breaking the law by being aboard the ship, they are in an isolated location on the ship which allows both the port and the ship to operate their normal business.
"We have considered various options and we have the skills, capabilities and equipment to deal with all options. However safety remains paramount and we won't needlessly jeopardise the safety of our staff, the crew of the ship or the protesters."
A member of the group tells the website, "The guys are well equipped and have enough food to last a couple of days and gear to protect them from the weather. We don't plan to leave until Shell agrees to stay out of the Arctic."