"It's been a tough couple of weeks, patience-wise. It's a bit of the other side of the coin for me - I'm used to being in a starting line-up in league and then coming back and having to be a bit more patient, not getting on against the Crusaders and then not being in the team the week after.
"So to get the opportunity to start, you've just got to take your opportunities and this is my chance.''
After playing as first five-eighth in his only appearance this season, Blues coach Sir John Kirwan said he had been impressed with the way Marshall had been training at fullback.
"We're keeping with the theme of really trying to create some internal competition and, although that's sometimes difficult to do when you haven't had a win, we believe in what we're doing,'' Kirwan said.
"We believe that Benji deserves a start at fullback - he's jumping out of his skin, he's ready to go, he's spent the last couple of weeks really refining that role so we'll put him in there.''
Charles Piutau moves from fullback to wing to accommodate the injection of Marshall, with youngster Tevita Li dropping out of the squad altogether.
After adding plenty of spark and scoring a try on debut last week, Pita Ahki is rewarded with a start at second five-eighth in place of Jackson Willison, while Chris Noakes replaces Simon Hickey at first five-eighths.
"Noakesy deserves another crack at it,'' Kirwan said. "We think he'll be really positive for us and he's ready and raring to go.''
In the forwards, Peter Saili is suffering from a patella tendon injury and Steven Luatua moves to the back of the scrum to replace him, with Brendon O'Connor getting his first start of the season at blindside flanker.
Patrick Tuipulotu replaces Liaki Moli at lock, while Jordan Manihera is poised to make his Super Rugby debut after being named on the bench.
Kirwan said the focus this week had been on keeping it simple, although he acknowledged the importance of heading home to New Zealand with points from the South African swing.
"It's not desperation time but if you want to be around at the end of the tournament then you've got to keep in touch with the leaderboard.''
The Blues team to face the Lions at Ellis Park on Sunday (NZT) is:
Benji Marshall, Frank Halai, George Moala, Pita Ahki, Charles Piutau, Chris Noakes, Piri Weepu, Steven Luatua, Luke Braid, Brendon O'Connor, Tom Donnelly, Patrick Tuipulotu, Charlie Faumuina, James Parsons, Tony Woodcock. Reserves: Tom McCartney, Sam Prattley, Angus Ta'avao, Liaki Moli, Jordan Manihera, Bryn Hall, Simon Hickey, Jackson Willison
