The Norwich City striker, out on loan at Rizespor, provided the quality to complement the hosts' control with two smart finishes in the first half to take his tally for the qualifying campaign to five.
Finland pulled one back in added time when Berat Sadik reacted quickest to a rebound in the box, but it was too little too late.
Michael O'Neill's side have now won four of their five Group F matches and sit just a point behind Romania.
This key fixture was staged against the backdrop of religious protests at the first international fixture to be played in the country on a Sunday.
But those who chose to attend left Windsor Park with no doubt about Northern Ireland's qualification credentials as they built a commanding lead before seeing out the second half with minimal fuss to bounce back from November's defeat to Romania.
O'Neill also increased the scrutiny on Finland coach Mixu Paatelainen - the man who gave him his coaching break at Cowdenbeath - as the visitors slipped to a third Group F defeat.
Northern Ireland's joint most capped outfield player, Aaron Hughes, had to settle for a place on the bench as Jonny Evans returned to competitive international action for the first time since October 2013.
There was good early tempo about the contest and the hosts had the ball in the net after just 10 minutes.
But Chris Baird's fantastic header was ruled out as Lafferty was judged to have been in an offside position when Chris Brunt delivered the cross, following a short corner one-two with Niall McGinn.
Jamie Ward missed a great opportunity to break the deadlock after 27 minutes, when he was denied by a reaction save from Lukas Hradecky, having been inadvertently teed up by Niklas Moisander.
Hradecky, however, could do nothing to keep out Lafferty's 33rd-minute opener.
Kasper Hamalainen only partially cleared Oliver Norwood's free-kick from the right and, when McGinn headed back into the danger area, Lafferty was there to steer into the far corner with a measured right-foot volley.
Lafferty's opener gave Windsor Park a real lift and the atmosphere was cranked up further when the striker doubled the lead five minutes later by using his size and positioning to pin down his defender and glance in Conor McLaughlin's wonderful right-wing cross.
Finland improved after half-time and could have pulled a goal back within six minutes of the restart.
Substitute Joel Pohjanpalo slid in at the front post and beat Roy Carroll to Sebastian Sorsa's low cross, only to divert it wide of the post.
Lafferty left the action to a standing ovation late on, having struggled with a knock in the second half.
Finland grabbed an unlikely consolation in the first minute of added time when Sadik, who appeared to be offside, pounced on a Carroll fumble from Roman Eremenko's long-range effort, but it would spoil Lafferty's day.
