The 27 year old, who played for Melbourne Storm in the 2024 NRL Grand Final, could make his Roughyeds debut against Sheffield at Boundary Park this weekend.
Vaalepu arrives at Roughyeds after featuring from the bench in each of Leigh's last four games following his move to the Leopards at the end of June.
The Penrith born forward made 11 appearances in Australia's NRL during his time with Melbourne Storm and was part of the side which faced Penrith Panthers in the 2024 Grand Final.
Before moving to the UK, Vaalepu had been playing for Melbourne's reserve side in the NSW Cup, where he averaged more than 100 running metres per game and recorded a tackle efficiency of 96 per cent.
He also has international experience after representing Samoa twice during their Test series against England in 2024.
Roughyeds have moved to strengthen their options in the pack as they prepare to face Sheffield at Boundary Park this weekend.
Head coach Alan Kilshaw said, "We're delighted to bring in Lazarus.
"We've been a little light on middle forwards over the last few weeks, so the timing of the move is really good for us.
"He'll add size, energy and competition to the squad at an important stage of the season.
"We'd like to thank Leigh Leopards for their support in making the deal happen, and we're looking forward to working with Lazarus."
Vaalepu will initially spend one week with the Roughyeds and is in contention to make his debut against Sheffield.
