Flintshire farmer Brynle Williams topped a poll of Conservative party members which was held to rank prospective candidates for the north Wales regional list.
Under the assembly election rules, this means Mr Williams, 53, would be all but guaranteed a list seat next spring, if he fails at first to take the Labour seat of Clwyd West in a traditional first-past-the-post vote.
He has stated his intentions to be an "honest speaker" for rural issues and to serve as a champion for north Wales.
While still supportive of direct action against high fuel prices, he said he had "seen the light" of working within the democratic system.
But Mr Williams' progress comes at the expense of the sitting AM Peter Rogers, who came seventh out of nine candidates, leaving him "shell-shocked and wounded".
The assembly's 20 list seats - a third of the total number of AMs - are decided on proportional representation and gave the Tories their only seats in north Wales at the 1999 elections.
Mr Williams, 53, hit the national headlines after leading the protest at the Stanlow oil refinery in Cheshire in 2000, which triggered protests across the UK, including Pembroke and Cardiff.
The Cilcain farmer only left the Stanlow blockade once during the two-week protest for his wedding anniversary.
Mr Williams said that he hoped to make an even bigger impact as an assembly politician.
"The best way to change the system is from the inside," he said.
"Direct action might get you a foot in the door, but I believe in democracy.
"I am very, very pleased and surprised at the result. It is the first step on a long journey. It was quite a surprise for a relative unknown in politics to come to the front."
Meanwhile, Peter Rogers knows he must now defeat Plaid Cymru leader Ieuan Wyn Jones to retain a seat in the assembly.
'Wounded'
"It is unbelievable," he said.
"I can't be very popular in my own party. I have had problems with the association. But my support has gone into freefall. I thought I might have dropped a place or two, but I am shell-shocked.
"It is not the end of the world, but I am going to graft now. The money was cracking for a farmer. But I am not sure if I will even keep my deposit now.
"I am wounded, but I will go out with my head held high."
Tory AM David Jones, who replaced former minister Rod Richards in the north Wales list seat, is not expected to stand for re-election next spring.