With his two children watching, Poincheval shut himself inside the 3.20 metre-high carving in the garden of the Aurignac museum in south-west France.
The museum specialises in prehistory and the original work, carved from a mammoth's tusk, is the oldest anthropomorphic sculpture known today, according to its director, Joëlle Arches.
It was created by some of the first homo sapiens to live in Europe.
"This lion is a sort of mirror for the men who lived 30,000 years ago," the 45-year-old artist said.
Poincheval enters the lion-man
Poincheval's previous "journeys in capsules" include:
A week inside a rock at Paris's Palais de Tokyo in 2017;
A week in a hole under rock weighing one tonne, also in 2017;
A week on a suspended platform near Paris's Gare de Lyon station in 2016;
Two weeks inside a stuffed bear in 2015;
A trip up the River Rhône in a six-metre-long bottle in 2015.