Second-placed Tottenham’s loss at West Ham last Friday and Chelsea’s 3-0 defeat of Middlesbrough on Monday meant the Blues needed three points from three games to clinch the championship.
Conte wanted to secure the trophy at the earliest opportunity and Batshuayi was an unlikely hero after 82 minutes at The Hawthorns.
Batshuayi was not even among the substitutes on Monday and is still to make a Premier League start.
The Belgium striker, a £33million signing from Marseille last summer, made his 18th Premier League appearance off the bench and finally showed his poacher’s instinct, seven minutes later, with his second league goal to send Chelsea and Antonio Conte delirious.
Chelsea had dominated possession, but the quality of their patient build-up was not matched by the final ball. And Albion caused the visitors some anxiety on the break.
The win saw Chelsea take an unassailable 10-point lead over Spurs with two games to spare and clinched the Blues’ fifth Premier League title in 13 seasons.
Chelsea had won once in five prior games here, in August 2015, and were defeated 3-0 two years ago after becoming champions in 2014-15 under Jose Mourinho.
The Blues imploded as seven months later Mourinho was sacked for a second time, before a 10th-placed finish behind Leicester last term.
Despite leading the rejuvenation, Conte’s future remains far from certain, with Inter Milan coveting the former Juventus and Italy boss. He now has four consecutive domestic titles after three with Juve.
The 47-year-old appears likely to be offered an improved contract, 12 months into the three-year deal he signed on joining last July, but on Thursday he suggested he wanted his “real value” to be recognised.
N’Golo Kante has been a key figure in Chelsea’s resurgence, but the midfielder had to settle for a place on the bench after recovering from a thigh problem as Chelsea were unchanged following Monday’s 3-0 defeat of Middlesbrough.
Kante was unused here, but he is the first player since Eric Cantona in 1992 and 1993 to win successive titles with different clubs.
John Terry was also not required, but the 36-year-old club captain will leave Chelsea this summer as a five-time Premier League champion.
Conte had warned Chelsea not to be complacent. And if they needed a further reminder it came in the opening seconds when Thibaut Courtois had to be alert to tip over a header from Salomon Rondon.
After Gary Cahill fired wide, Diego Costa had an effort blocked and Pedro shot over, James McClean led a Baggies counter attack.
Pressure from a back-tracking Eden Hazard forced McClean to relinquish possession.
Deflected efforts from Pedro and Cesar Azpilicueta forced a succession of corners before McClean burst down the right again. Chelsea dealt with the danger again.
Cesc Fabregas was pulling the strings, as he had against Boro. He fired narrowly wide across goal while Pedro turned on the edge of the area and curled wide soon afterwards.
And next Costa turned Jonny Evans before lifting the ball over. Evans also escaped censure for a bizarre handball when holding off Fabregas.
David Luiz intercepted McClean’s cross intended for Chris Brunt as the half ended goalless.
Foster saved well to turn Moses’ effort away for a corner and Fabregas shot wide as Chelsea resumed on the attack.
A Hazard cross was diverted towards his own goal by Craig Dawson, but substitute Claudio Yacob blocked.
Costa pirouetted into Yacob after turning to avoid Gareth McAuley, but his appeals for a penalty were ignored by referee Michael Oliver.
Another Albion counter was snuffed out as Azpilicueta pressurised Rondon.
There was a better opportunity soon afterwards for Nacer Chadli, once of Tottenham, but the substitute missed the target.
Hazard and Pedro were replaced by Willian and Batshuayi as Chelsea sought a different threat with 15 minutes to go.
And Batshuayi pounced when Cahill’s sliced shot was centred by Azpilicueta to spark celebrations which had to wait a few more minutes.
Albion sought an equaliser, but Chelsea held on to clinch a deserved title.