The boys were 10 and 13, and had been pulled about 50m down the beach by the rip.
Between Mr Newell and the other beachgoer they pulled the pair to safety.
One was wearing a t-shirt in the water which Mr Newell said was a "no-no" as they became heavy when wet.
"If I wasn't there and those other beachgoers weren't there it could have been fatal."
Mr Newell said people needed to be aware of the dangers at Whanganui's beaches.
"You can see the rips. It's about knowing what to look for and being supervised."
The Whanganui Surf Lifeguard Service, of which Mr Newell is a member, begins daily patrols at Castlecliff and Kai Iwi Beach from December 16.
Patrols will run from 12pm to 6pm until the end of February.
On opening day the club will be unveiling and sponsor's day for the new lifeguard shelter at Kai Iwi beach.
At the two beaches last summer surf lifeguards performed more than 4000 preventive and no rescues.
"Although this is good for Whanganui with no rescues we are always trying to improve and evolve ourselves it is still clear that the need for the public intervention is necessary," club media liaison Daniel Comp said.
Mr Comp said rips were a problem at both beaches and people often overestimated their ability and underestimated the risk.
"Take a moment to stop and think before entering the water and if in doubt stay out."
At Castlecliff beach there are constant rip currents that begin from the north of the club house heading towards the south mole and at Kai Iwi Beach the streams at both ends provide a strong undertow at high tide which beachgoers and swimmers need to be aware of.
Anyone who finds themselves caught in a rip should lie on their back and raise their hand to signal for help. Try to fight the urge to swim against the current as this will use up energy that you need to stay afloat.
If you spot someone in a rip at an unpatrolled beach, ensure your own safety and call 111 and ask for Police.
