Wright, in only his third game since giving up the captaincy, made 118, his best score since he hit a career-best 226 against Worcestershire in September 2015. It was also his first hundred at Hove for two days shy of two years.
With his successor as captain Ben Brown making 52 and Chris Jordan 50, Sussex recovered from 69 for 3 to post 358 for 9 declared.
They then had seven overs in the twilight with the pink ball but Gloucestershire openers Cameron Bancroft and Chris Dent got through unscathed, reaching 31 for 0 at stumps.
A crowd of 2,000 was boosted by around 650 local schoolchildren and they enjoyed an entertaining day with Wright leading an aggressive counter-attack by Sussex during the afternoon session when they plundered 173 runs.
Wright was in the mood from the very start, lofting his first ball from off-spinner Jack Taylor for one of three sixes. There were also 14 fours including a straight drive to the boundary which brought up the 17th century of his first-class career.
The way Wright, and later Brown and Jordan, stroked the pink ball over a fast outfield was in contrast to what happened at the start of the day and again when Gloucestershire took the new ball and immediately claimed three wickets.
Fit-again Liam Norwell and David Payne were rewarded with a wicket apiece as Harry Finch and Delray Rawlins, opening after Chris Nash was struck in practice and suffered a concussion, departed cheaply.
Luke Wells hit seven fours in his 36 before Taylor had him caught at slip, after the ball had deflected off wicketkeeper Gareth Roderick.
Wright then transformed the day, first with Stiaan van Zyl with whom he added 99 in 19 overs before the South African was held at short leg off Taylor, and then alongside his successor as captain.
If anything, Wright and Brown increased the tempo. Both attacked anything off line and the ball had to be changed after 54 overs after Wright had clattered it into the protective covers beyond the boundary.
His hundred came up off exactly 100 balls while new skipper Brown, returning after six weeks out with a broken finger, matched him shot for shot as they put on 92 in 18 overs. Brown fell two balls after reaching 50 from 60 deliveries with seven fours and a six and Wright departed after tea to a brilliant one-handed catch at mid-wicket by Phil Mustard, his 118 coming off 129 balls.
David Wiese and Chris Jordan took the attack back to Gloucestershire, adding 57 in 13 overs for the seventh wicket but the new ball swung markedly as the floodlights took effect and Gloucestershire picked up three quick wickets, Craig Miles taking two of them in the same over including Jordan for a 78-ball 50 with eight fours.
Sussex declared shortly after claiming a fourth bowling point but couldn’t make a breakthrough before the close.
Wright said: "Walking down the steps going out to bat I was determined to play my own game and if that meant hitting the off-spinner for six first-ball if that opportunity came I’d do it – and I did!
"I spent most of last season injured so I didn’t get many opportunities to bat like that. Since giving up the captaincy, which was a very difficult decision for me to make, I’ve tried to enjoy myself and play with freedom.
"The pink ball definitely did more when it was new and it’s a shame we couldn’t get a wicket or two at the end after declaring but credit to their openers, they got through it well.
"We’re happy with 350 but there were a few soft dismissals in there as well so maybe we could have done even better but our bowlers will be fresh in the morning and we can come hard at them again."
Gloucestershire coach Richard Dawson said: "I thought we bowled really well in the first session, not so well in the middle and then dragged it back at the end with the second new ball.
"We told our guys to be aware that they might declare and have a few overs at us before the end but I thought the way our openers got through those seven overs was excellent – they did really well and hopefully have set us up for a good day on Tuesday."