The 26-year-old was already signed connected for adjacent season, and is present locked into the nine until conscionable earlier his 31st birthday.
"I'm stoked to beryllium staying astatine the nine for a further 3 years and hopefully it's different measurement successful staying arsenic a one-club player," Johnston said.
"The past mates of years person been monolithic and I'll beryllium doing everything I tin to guarantee we spell 1 measurement further than we did this twelvemonth and triumph much premierships for this club."
After debuting successful 2014 and scoring a effort successful Souths' drought-breaking rubric triumph that year, Johnston has been a fixture, mostly connected the near wing, portion besides playing fullback astatine assorted points passim his tenure.
He has topped the tryscoring charts successful each of the past 2 NRL seasons, and is apt to walk nine fable Nathan Merritt precise soon arsenic the antheral who has scored the astir ever tries for the Rabbitohs.
Merritt crossed the stripe 146 times successful his clip astatine South Sydney, with Johnston presently astatine 136.
Given his age, fans and pundits alike person already started to murmur that Johnston could perchance eclipse Ken Irvine (212 tries) arsenic the top successful the past of the game.
If helium continues playing connected Souths' potent near edge, he's each chance.
Sterlo's Wrap: Grand Final recap & Sterlo's Final Word
Johnston astir near the nine past year, helium said helium was pleased to benignant his aboriginal retired truthful rapidly this clip around.
"I joked with 'Ello' [Souths caput of shot Mark Ellison] that I wanted to beryllium the archetypal to re-sign this clip astir and it's large to person it each sorted retired bully and early," Johnston said.
The signing comes connected the backmost of prop Mark Nicholls extending his declaration past week, and volition beryllium euphony to the ears of fans - who were near stunned that Johnston was astir allowed to permission the club.
The quality volition beryllium immoderate much-needed tonic for Souths fans aft suffering a expansive last defeat, and the departure of different section inferior successful Adam Reynolds.
"Alex is simply a tremendous finisher and is truly gathering the different areas of helping play specified arsenic footwear returns and defence," Ellison said.
"He is simply a arrogant Indigenous antheral that roseate to the Rabbitohs from La Perouse successful the Souths Juniors competitions and has gone connected to correspond Australia, Papua New Guinea and the Indigenous All Stars truthful acold successful his career."
"He is simply a fashionable subordinate of the squad and is becoming 1 of the starring elder players astatine the club," Ellison said.
"We're precise excited to beryllium capable to widen his declaration for a further 3 years connected apical of his existing declaration and look guardant to seeing him people galore much tries successful that near country successful the years to come."
For a regular dose of the champion of the breaking quality and exclusive contented from Wide World of Sports, subscribe to our newsletter by clicking here!