Swedes Christian Nilsson and Steven Jeppesen are tied for third place with Benn Barham at minus-5.
Frenchman Thomas Levet, who has missed the cut in 10 of 16 starts in his national Open, is alone in seventh place at 4-under-par 67 on the Albatross Course at Le Golf National.
Sullivan, who played in the final group off the first tee, packed all the action into the middle of his round. He started with a birdie on the par-4 fifth.
The 31 year old collected back-to-back birdies from the par-3 eighth to make the turn at minus-3.
Sullivan converted his fourth birdie on the par-3 11th. After a par at the next, the Welshman birdied the 13th and came right back to birdie No. 14 to grab a share of the lead at minus-6. He parred the final four holes to close out a bogey-free round.
'I have played with James on the Challenge Tour and it's good to see guys from that tour doing well,' Sullivan stated. 'It gives you the encouragement to kick on and believe you can lead an event like the Open de France.'
Kamte, who got into the field via a 36-hole qualifier, played the back nine first and had an up-and-down nine. He made a birdie effort on the 11th. After dropping a shot on the par-4 13th, he got that stroke right back with a birdie on 14.
The South African birdied the 17th, but gave that shot back as he bogeyed 18 to make the turn in 1-under.
Around the turn, Kamte turned it on. He birdied the par-three second and jumped to four-under with an eagle at the par-5 third. Birdies on the sixth and eighth gave him a piece of the lead.
Kamte has Ernie Els to thank for the shape of his game.
'If I ever win one of these big events I will thank Ernie right there on the spot,' Kamte admitted. 'He gave me the opportunity to play back home through his Foundation when no one else would give me the opportunity. If it wasn't for him, I wouldn't be sitting here today.'
Eight-time Order of Merit champion Colin Montgomerie opened with a 3-under-par 68. He was joined in a share of eighth place by Frenchman Raphael Jacquelin as well as Damien McGrane, Thomas Bjorn, Markus Brier, Miguel Angel Martin, Jyoti Randhawa, Zane Scotland and Jose-Filipe Lima.
Among the eight players one stroke further back are Miguel Angel Jimenez, Paul McGinley and France's Gregory Havret.
Defending champion John Bickerton is tied for 38th after an even-par 71.