But a thigh injury wreaked havoc, initially delaying and then ending the then 20-year-old's trip.
This time Halfpenny, the 2013 RBS Player of the Championship and newly crowned Welsh Rugby Writers Player of the Year, is determined to play a leading role Down Under.
"It's special to be part of a Lions team, it's what you dream of growing up as a kid and I'm so happy to be going again," said Halfpenny.
"That tour in 2009 was totally unexpected. If somebody had told me at the beginning of the season that I would be going I wouldn't have believed them.
"It was a great experience and something I learnt a massive amount from. I enjoyed my time but I was absolutely gutted to have to leave through injury.
"Having to come home early was absolutely devastating. But having experienced it and seen how special it is only makes me hungrier.
"This time round I have a lot of experience at international level and I'm really looking to doing the best I can for the Lions."
Since watching Jason Robinson and Brian O'Driscoll waltz past the Wallabies in 2001, Halfpenny has been infatuated with the famous tourists.
And despite being a near shoo-in for selection for a second stint, the humble 24-year-old has been blown away by his inclusion.
"It was a pretty emotional experience and to hear my name read out first was a huge relief," added the Cardiff Blues star.
"I've done everything possible to go on this tour. A lot of hard work has gone in all year and I'm really chuffed to be in this position.
"My first real Lions experience was watching the 2001 tour of Australia -there are so many great memories from that series.
"Jason Robinson going around Chris Latham with just two or three yards space and the passion he showed after scoring and how the stadium erupted. Brian O'Driscoll going through a gap that wasn't even there. It was incredible."
But if there was one thing Halfpenny learnt from watching the 2001 tour it was to never write a Wallaby off.
He has since faced the Wallabies on seven occasions and all seven encounters have ended in more misery.
Last summer Wales lost all three Tests by a combined total of 11 points and in the autumn he was knocked out as Kurtley Beale snatched yet another last-gasp victory.
But Halfpenny is adamant the Lions can take confidence from Wales' agonising defeats and record a first series victory since 1997.
"That tour showed the Aussies are a quality outfit and they will be a tough team to beat again," added the deadly goalkicker.
"It will be a difficult series but we can be confident.
"They can't take it for granted that they have beaten Wales so they will beat the Lions. For the Welsh players, we have experienced it in the summer and we can take confidence from how close we got.
"I'm sure we will be successful Down Under."