Mr Johnson has taken a hardline stance on leaving the EU by the end of October, as well as refusing to rule out ignoring MPs and proroguing Parliament to ram through a no deal should he fail to win support.
When asked if this was the best approach to Brexit as she arrived for her final European Council summit, Mrs May said the next prime minister should focus on getting a deal through Parliament.
She said: “I’ve always been very clear that I think the best approach for the UK is to first of all ensure we’re delivering on the vote that took place in 2016, leaving the EU, but that we do that with a good deal so we can do it in an orderly way.
“I still think we negotiated a good deal, I wasn’t able to get a majority in Parliament for that deal.
“It will be up to my successor to get that majority, deliver on the vote and take us forward.”
Appearing cheerful as she walked the red carpet into a Brussels summit for what is expected to be her final time, Mrs May said she was proud of what she had achieved, particularly around security threats and environmental issues.
She said: “Of course we have had some tough and long talks about Brexit.
“We have also talked about how we will protect and maintain our shared prosperity and security.
“So for example when we saw chemical weapons used on the streets of Salisbury there was a very strong and powerful unified message sent from the UK and the 27 other member states of the EU through the expulsion of many so-called Russian diplomats.
“The UK has also been leading on the issue of climate change where we need to ensure we have a better environment for the future.”
Mrs May added she was looking forward to a “constructive discussion” on who should take up the top jobs in the EU institutions.
Stressing the importance of security, she added: “Of course, once we leave the EU our relationship with the 27 member states will continue to be important.
“They are our closest neighbours and we will continue to be facing the same challenges and wanting to work together protecting our values.”
Additional reporting by Press Association