Former Wales full back Hayward has been involved in the Wales junior set up over the last few years as attack coach but steps up to head coach in place of Danny Wilson.
Wilson, who led Wales to the Junior World Championship final in France last month, has completed his two year contract and will now concentrate on his role as forwards coach at the Scarlets.
"Obviously being involved over the last two years makes me aware of the challenges I'll have to deal with," said Hayward after being announced as the new head coach.
"I've had experience of working with these coaches and hopefully that exposure, particularly working with Danny, will stand me in good stead.
"It's a tough act to follow, I guess we'll have to try to get to the final again next year and win it! The transition will be quite seamless really but it is a different role."
Hayward will lead Wales into the Six Nations and next year's Junior World Championship following a hugely successful past 12 months.
Under Wilson, Wales finished second in this year's Six Nations and reached the final of the Junior World Championship in France, beating Argentina and South Africa on the way.
"Last year was the first time we beat New Zealand and that helped to dispel the myth of the Southern Hemisphere sides if you will," added Hayward.
"That's been put to rest now which is a massive step forward for us.
"We now have the belief we can beat these teams and what happened last year was a huge factor in that."
Speaking at yesterday's announcement at the WRU Centre of Excellence, Gethin Watts, WRU National Performance Manager, added: "It's a privilege and a pleasure to announce Byron Hayward as the new Wales Under 20 head coach.
"Byron is a former international and if he doesn't mind me saying it, a seasoned pro. He's coached at regional level with Sale so it's certainly no step down."
Hayward will continue to work alongside team manager Mark Taylor, defence coach Richard Hodges and Ioan Cunningham, who steps up from the Wales Under 18 side.
Watts added: "The Wales Under 20 side have had some great success recently and I would like to pay tribute to Danny Wilson for his expertise in guiding them to the success of the last few years.
"Continuity has been at the forefront of our minds and Byron will continue that work alongside Richard Hodges and Ioan Cunningham. We believe we have a strong team which will continue to make us successful in the next few years."