Bilic’s side will join Championship title winners Leeds in the top-flight next season after a nail-biting Wednesday night at the Hawthorns.
With third-placed Brentford beaten 2-1 by Barnsley and fourth-placed Fulham held to a 1-1 draw at Wigan, Albion finished in second place to secure their return to the Premier League after two seasons away.
“You don’t know how exhausting it was this season. You can’t imagine how proud and happy I am,” former Croatia and West Ham boss Bilic said.
“I managed my country for six years and I said no matter which club I manage nothing will compare. I feel as proud as I felt then.”
On a riveting finale in the second tier, 2013 FA Cup winners Wigan were relegated to League One along with Hull and Charlton.
But the focus was on West Brom, who fell behind against QPR when Ryan Manning netted after 34 minutes.
Grady Diangana equalised just before half-time when he fired in after Callum Robinson set him free.
The Baggies went in front early in the second half when Diangana’s cross found the unmarked Robinson to tap in.
QPR weren’t making it easy for West Brom and the tension mounted after Eberechi Eze lashed a 61st minute equaliser into the top corner.
West Brom’s attention turned to Griffin Park, where Brentford were unable to take advantage as they chased a first season in the top-flight in 73 years.
– West Brom joy –
Brentford, who missed a chance to go second when they lost at Stoke on Saturday, found themselves trailing when Barnsley’s Callum Styles struck in the 40th minute.
With West Brom drawing, a victory would have taken Brentford up and Josh Dasilva equalised in the 72nd minute.
But in stoppage time, Clarke Oduor tapped in Barnsley’s winner and news quickly spread to the Hawthorns, where Bilic implored his players to defend the point that would take them up.
“What a season, what a league. I didn’t enjoy every minute of it, of course, but with a finish like this, the results at the bottom, it’s unbelievable,” Bilic said.
“I thought Brentford would have pressure in today’s game. It’s not easy. That’s why I’m very proud of the boys.”
Barnsley’s surprise victory lifted them out of the relegation zone in the most dramatic fashion.
Brentford will have to pick themselves up for the play-offs, where they will face a two-legged semi-final against Swansea, who made a stunning climb into sixth place with a 4-1 win at Reading.
“We can’t sit down and cry too long because that will never help anything,” Brentford boss Thomas Frank said.
“We will have a sleep and then be ready to fight again.”
Swansea took the place of Nottingham Forest, whose 4-1 home defeat against Stoke knocked them below the Welsh club on goal difference.
The other play-off semi-final will see Fulham face fifth placed Cardiff, who eased to a 3-0 win over bottom of the table Hull.
Troubled Wigan are relegated following the end-of-season deduction of 12 points for going into administration earlier this month.
The Latics, who were last in the Premier League in 2013, had reached 59 points, but the deduction reduced their total to 47, which left them in the relegation zone.
Wigan have appealed against the points penalty, which was triggered when the controversial sale of the club left them in the hands of new owners, who immediately opted to go into administration.
“I feel physically sick for everyone. I don’t want to talk about the appeal because the reality is, we shouldn’t be in this situation,” Wigan boss Paul Cook said.
Charlton went down after a 4-0 thrashing at Leeds, who were presented with the Championship trophy — their first silverware since 1992.
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