diff --git a/changelog/4425.bugfix.rst b/changelog/4425.bugfix.rst
new file mode 100644
index 000000000..7c869cd4c
--- /dev/null
+++ b/changelog/4425.bugfix.rst
@@ -0,0 +1 @@
+Ensure we resolve the absolute path when the given ``--basetemp`` is a relative path.
diff --git a/src/_pytest/monkeypatch.py b/src/_pytest/monkeypatch.py
index d536b7746..2c81de177 100644
--- a/src/_pytest/monkeypatch.py
+++ b/src/_pytest/monkeypatch.py
@@ -13,8 +13,9 @@ import six
 
 import pytest
 from _pytest.fixtures import fixture
+from _pytest.pathlib import Path
 
-RE_IMPORT_ERROR_NAME = re.compile("^No module named (.*)$")
+RE_IMPORT_ERROR_NAME = re.compile(r"^No module named (.*)$")
 
 
 @fixture
@@ -267,6 +268,9 @@ class MonkeyPatch(object):
             self._cwd = os.getcwd()
         if hasattr(path, "chdir"):
             path.chdir()
+        elif isinstance(path, Path):
+            # modern python uses the fspath protocol here LEGACY
+            os.chdir(str(path))
         else:
             os.chdir(path)
 
diff --git a/src/_pytest/tmpdir.py b/src/_pytest/tmpdir.py
index 6287c1705..81430e4f0 100644
--- a/src/_pytest/tmpdir.py
+++ b/src/_pytest/tmpdir.py
@@ -26,7 +26,9 @@ class TempPathFactory(object):
 
     The base directory can be configured using the ``--basetemp`` option."""
 
-    _given_basetemp = attr.ib()
+    _given_basetemp = attr.ib(
+        convert=attr.converters.optional(lambda p: Path(p).resolve())
+    )
     _trace = attr.ib()
     _basetemp = attr.ib(default=None)
 
@@ -53,7 +55,7 @@ class TempPathFactory(object):
         """ return base temporary directory. """
         if self._basetemp is None:
             if self._given_basetemp is not None:
-                basetemp = Path(self._given_basetemp)
+                basetemp = self._given_basetemp
                 ensure_reset_dir(basetemp)
             else:
                 from_env = os.environ.get("PYTEST_DEBUG_TEMPROOT")
diff --git a/testing/test_tmpdir.py b/testing/test_tmpdir.py
index 38b0672b7..fddece2cf 100644
--- a/testing/test_tmpdir.py
+++ b/testing/test_tmpdir.py
@@ -4,6 +4,7 @@ from __future__ import print_function
 
 import sys
 
+import attr
 import six
 
 import pytest
@@ -25,12 +26,29 @@ def test_ensuretemp(recwarn):
     assert d1.check(dir=1)
 
 
+@attr.s
+class FakeConfig(object):
+    basetemp = attr.ib()
+    trace = attr.ib(default=None)
+
+    @property
+    def trace(self):
+        return self
+
+    def get(self, key):
+        return lambda *k: None
+
+    @property
+    def option(self):
+        return self
+
+
 class TestTempdirHandler(object):
-    def test_mktemp(self, testdir):
+    def test_mktemp(self, tmp_path):
+
         from _pytest.tmpdir import TempdirFactory, TempPathFactory
 
-        config = testdir.parseconfig()
-        config.option.basetemp = testdir.mkdir("hello")
+        config = FakeConfig(tmp_path)
         t = TempdirFactory(TempPathFactory.from_config(config))
         tmp = t.mktemp("world")
         assert tmp.relto(t.getbasetemp()) == "world0"
@@ -40,6 +58,15 @@ class TestTempdirHandler(object):
         assert tmp2.relto(t.getbasetemp()).startswith("this")
         assert tmp2 != tmp
 
+    @pytest.mark.issue(4425)
+    def test_tmppath_relative_basetemp_absolute(self, tmp_path, monkeypatch):
+        from _pytest.tmpdir import TempPathFactory
+
+        monkeypatch.chdir(tmp_path)
+        config = FakeConfig("hello")
+        t = TempPathFactory.from_config(config)
+        assert t.getbasetemp() == (tmp_path / "hello")
+
 
 class TestConfigTmpdir(object):
     def test_getbasetemp_custom_removes_old(self, testdir):