Stuart Anderson maintained the PM was "the right person to run the country" but said he was left with no choice but to stand down after so many Cabinet ministers quit.
Meanwhile Lichfield MP Michael Fabricant, another big supporter of Mr Johnson, warned MPs they could come to regret the move to oust him in the years to come.
MPs across the Black Country and Staffordshire have been reacting to Mr Johnson's decision to leave Number 10, which was confirmed on Thursday morning after a tidal wave of ministerial resignations.
Mr Johnson is set to stay in post until autumn, when a new Prime Minister will take over following a Conservative Party leadership election.
It came as the campaign to replace him kicked into gear, with Gavin Williamson moving to deny reports he was backing Nadhim Zahawi's bid for the top job.
Wolverhampton South West MP Mr Anderson, who stayed loyal to Mr Johnson throughout, told the Express & Star: "It's a sad day. I stayed loyal to Boris because I think he is the right person to run the country.
"In the end we weren't able to command the numbers and we no longer had a functioning Government, so he did the right thing and resigned.
"When you can't run the country you need a change at the top."
Mr Anderson said he had not yet decided who to back in the leadership contest, which will take place in the coming weeks.
He said: "I'll wait to see who is running, who is best for Wolverhampton and make a decision on that."
Mr Fabricant told the Star: "It was sadly inevitable with so many resignations that the Prime Minister was going to have to resign.
"The transition to his replacement will be messy and long-winded. I hope that those who agitated so hard for Boris Johnson's removal will not come to regret it in the years to come."
Asked who he would back in the leadership election, Mr Fabricant said: "It's too early. The Prime Minister is still warm and not in his coffin yet."
Stourbridge MP Suzanne Webb said she was "very sad and very disappointed" that Mr Johnson was on the way out.
"However, I do understand the Prime Minister’s position had become impossible," she told the Star.
"Boris Johnson has achieved much in some of the most challenging times this country has faced in generations. Getting Brexit done, dealing with a pandemic, and facing down Putin over his invasion of Ukraine.
"And this leads me to an important point. My junior role in Government is Parliamentary Private Secretary at the Ministry of Defence.
"I was never going to resign from my position while Putin remains in Ukraine. My loyalty is to the Defence Secretary and his vital work keeping this country safe.
"The country comes first every time. It’s now time to move on. My primary focus now is continuing to do all I can for the people of Stourbridge."
Dudley North MP Marco Longhi has had his say on the PM's departure. He has been a vocal supporter of Mr Johnson, but has called him out for not delivering on key manifesto pledges during his tenure.
Mr Longhi said: "My loyalties, first and foremost, are to the people of Dudley North. In my maiden speech in the House of Commons I vowed to help Dudley get the best deal possible, to future-proof our local economy, boost jobs, and improve health.
"None of us would have expected the pandemic (or a war in Europe), but now we find ourselves coming out the other end, we need to all knuckle down together to deliver on our manifesto pledges. I want to thank Boris Johnson for delivering Brexit and dispelling the possibility of a Corbyn government and leading us out of Covid.
"My plans for Dudley remain unchanged. I want to see footfall increased in a renewed High Street, see police regain control of law and order and for us to retain our focus on skills and protect our greenbelt.
"I want to see the new Dudley super police station finally delivered, ending years of dither and delay, and I want to see an end to illegal immigration, especially on the horrendous people smuggling boats coming across the English Channel.
"I have had enough, you have had enough, more robust and direct action is needed now.
"The next leader of the Conservative Party, and ultimately, Prime Minister, will need to be someone who delivers on our manifesto pledges, who understands the needs of places like Dudley North, and who is willing to make the tough decisions to make things happen.
"Whoever that ultimately is, will have my unfaltering loyalty to deliver, just as the previous PM deserved it."
Halesowen & Rowley Regis MP James Morris said: "The Prime Minister got Brexit done, led our party to its largest majority since the ‘80s, guided us through Covid-19 and has led the international response to the Ukrainian crisis.
"He had much to be proud of, and I wish him and his family well for the future."
West Bromwich East MP Nicola Richards, who resigned as a PPS on Tuesday, said she was grateful to Mr Johnson for his achievements in office.
She added: "I'm glad he has now recognised that it is time to step aside so the country can have the fresh leadership it so desperately needs."
Labour has called for Mr Johnson to "go now" rather than wait until the autumn, saying he had "no authority to continue" in office.
Wolverhampton South East MP Pat McFadden, Labour's Shadow Treasury Secretary, told the Star: "It is right that the Prime Minister is resigning.
"No Prime Minister in modern times has debased the office more and eventually even his own MPs couldn't stand it.
"But while all this is going on people still face a cost of living crisis, many don't know how they will make ends meet and the country faces big challenges.
"We need to end the chaos and have a Government that can help the country through this period and put in place a better long term plan for the future."
He added: "Now that the decision has been made the PM must go now. He has no authority to continue."
John Spellar, Labour MP for Warley, has also called for Mr Johnson to depart with immediate effect. He said: "It was inevitable, but it's really a shame the country has to be put through this Boris Johnson psycho-drama.
"It's not just about all the bad behaviour, but frankly how badly the country is being run.
"So many central Government services are collapsing and ministers seem unwilling and incapable of getting a grip and responding to it.
"Let's hope the new leader will address that, but again let's decide this at the ballot box and set this country on a new course."
He added: "He should go now. They should appoint an interim Prime Minister and in the autumn they can always speed up the process. Why should the country have to pay for this?
"It is ridiculous. We need a new Prime Minister to start a new direction for the Government and for the country.
"They should put an interim Prime Minister in place and Johnson should be packing his bags as we speak."
