The Eagles completed a deal for the versatile operator yesterday, and he joined up with his new team mates for the first time at training last night.
Aston, who has signed nine players during the close season, has further bolstered his numbers with the arrival of Johnson, who penned a two-year contract extension with the Super League outfit in July last year.
“We have been keen on bringing this lad to Sheffield Eagles for some time,” director of rugby Mark Aston told www.sheffieldeagles.com
“We are all about competition for places here at this club, and with Liam’s versatility he will certainly add that in a number of key areas.
“We are really pleased to have finally got him because to be honest this was a deal that we almost had done a couple of weeks ago, so it is great to get this one over the line and get Liam through the door.”
The second-rower, who can also operate at loose forward and at centre, has Championship experience from a spell with Oldham last season, where he made 19 appearances for the Roughyeds.
Johnson has also captained England at youth level.
“We have had a good look at him, we saw him play for Oldham last season, and we like what we have seen,” Aston maintained.
“He fits in well to the type of player that we like to have at this club. He is young with lots of potential, and this is a project that we can develop.
“He had taste of The Championship last season, where he had some success but now he needs to kick on.
"He has talent and I think he will thrive in our environment because we now have some depth in a number of areas, and that will bring on others who are already in the group.
“Obviously we thank Huddersfield for trusting us with his development, and we look forward to seeing him in an Eagles jersey.”
The Eagles are back in action this Sunday when they take on Halifax at The Shay, kick off 3pm.