Arsene Wenger’s side booked their place in Europe’s elite club competition without kicking a ball when fifth placed Everton were beaten 3-2 by Manchester City on Saturday.
And 24 hours later, Giroud’s first half header maintained the feel-good factor at the Emirates Stadium and capped a stroll in the sunshine for the Gunners, who were rarely troubled en route to a fourth successive victory.
After looking in severe danger of missing out on the Champions League for the first time in 17 years following their defeat at Everton last month, there was a palpable sense of relief in north London that Arsenal had wrapped up fourth place with two games to spare.
Albion never threatened to spoil the party, but Pepe Mel’s team remain four points above the relegation zone and their safety will be guaranteed if third bottom Norwich lost either of their final two matches against Chelsea and Arsenal.
With influential midfielder Aaron Ramsey sidelined by a thigh injury and Arsenal’s Champions League mission already complete, it would have been no surprise to see the Gunners go through the motions.
But the incentive of nailing down places in the team for the FA Cup final against Hull on May 17 ensured there was sufficient spark to Arsenal’s play and they quickly forced Albion onto the back foot.
The Gunners threatened in the opening moments when Lukas Podolski fired wide of the near post from Giroud’s flick.
Albion couldn’t cope with the speed and precision of Arsenal’s attacks and Mesut Ozil slalomed into the penalty area before setting up Santi Cazorla for a powerful shot that deflected over.
Arsenal’s pressure was rewarded from the resulting Cazorla corner in the 14th minute as France striker Giroud, showing greater desire than his Albion markers, made a thrusting run to the near-post where he directed a close-range header past Ben Foster.
Giroud’s 22nd goal of the season should have acted as a wake-up call for lethargic Albion, but instead another defensive error, this time from Diego Lugano, almost led to a second goal.
Mathieu Flamini seized on the loose ball and with Giroud lurking with a intent in the six-yard box it was only Foster’s smart save with his legs that averted the danger.
At least Albion defender Craig Dawson was willing to put his body on the line to keep the Gunners at bay and he gamely blocked Flamini’s strike in a particularly sensitive area just below his midriff.
Albion’s tepid efforts to close down the hosts allowed to Arsenal dominate possession and their lone striker Saido Berahino had only one sight of goal, a ferocious effort from the edge of the area which fizzed just over.
That was a rare moment of concern for Arsenal and Cazorla almost doubled their lead moments later, but Foster plunged low to his right to keep out the Spaniard’s goalbound strike.
Wenger’s side lacked their first half verve and almost paid the price when Morgan Amalfitano burst through, only for Per Mertesacker to make a last-ditch challenge.
Dawson went close to equalising with a header from a corner and Amalfitano brought a fine save from Wojciech Szczesny, but it was Arsenal who had the best chance of a soporific second half when Podolski scuffed his shot onto a post.
With the points in the bag, the celebratory mood continued after the final whistle as Arsenal’s players marked their final home game of the season with a lap of honour featuring chants from fans for French right-back Bacary Sagna to ignore reported interest from Manchester City and sign a new contract.