The New Zealand native, along with six other activists with Greenpeace, were sentenced Thursday for illegally boarding and occupying a drillship bound for the Arctic in February 2012.
Each of the seven activists was assigned 120 hours of community service and fined about $500, One News reported.
The group avoided paying a fine of nearly half a million dollars to Shell, which owns the ship Noble Discoverer, with Judge Allan Roberts of the New Plymouth District Court calling such a fine unfair in a criminal case.
Lawless called the outcome of the sentence a victory, since it helped raised the profile of Shell's Arctic drilling efforts.
"Since we occupied the Noble Discoverer, it has become evident to everyone watching, from the millions who have signed Greenpeace petitions, to the US Government, now examining Shell's plans, that it can never be safe to drill in the Arctic," Lawless said outside the courthouse.
"Shell's Arctic program has cost them billions and it's now regarded as an eye-wateringly expensive failure."
Lawless and the other six activists, five of whom are New Zealanders and one who is from Spain, breached security at Port Taranaki in February 2012 and climbed onto the ship, camping out on its drilling rig for 77 hours and delaying its scheduled departure for the Arctic.
They were originally charged with burglary, but agreed to plead guilty to charges of illegal boarding in June.
In a statement, Shell Todd Oil manager Rob Jager said he hoped the action would deter similar protests in the future.
"Shell Todd Oil Services recognizes the right of individuals to express their point of view and protest in a manner that does not place the safety of people or property at risk," Jager said in a statement. "We continue to extend our offer of an open conversation where there is a real desire to find solutions."
Shell and its Arctic drilling operations have been a constant target of Greenpeace, which has launched multiple campaigns in an effort to halt drilling in environmentally sensitive waters. Two in particular--a viral social advertising campaign hoax and a fake launch party gone wrong--were particularly high profile.