diff --git a/.changes/unreleased/Features-20230119-141156.yaml b/.changes/unreleased/Features-20230119-141156.yaml
new file mode 100644
index 00000000000..dde705b05c5
--- /dev/null
+++ b/.changes/unreleased/Features-20230119-141156.yaml
@@ -0,0 +1,6 @@
+kind: Features
+body: add support for DBT_PROJECT_DIR env var
+time: 2023-01-19T14:11:56.638325919+01:00
+custom:
+  Author: leo-schick
+  Issue: "6078"
diff --git a/core/dbt/cli/params.py b/core/dbt/cli/params.py
index 3ad3747e962..73532eb9a70 100644
--- a/core/dbt/cli/params.py
+++ b/core/dbt/cli/params.py
@@ -219,7 +219,7 @@
 
 project_dir = click.option(
     "--project-dir",
-    envvar=None,
+    envvar="DBT_PROJECT_DIR",
     help="Which directory to look in for the dbt_project.yml file. Default is the current working directory and its parents.",
     default=default_project_dir(),
     type=click.Path(exists=True),
diff --git a/core/dbt/config/runtime.py b/core/dbt/config/runtime.py
index b0b74b9a222..05cbbff15b5 100644
--- a/core/dbt/config/runtime.py
+++ b/core/dbt/config/runtime.py
@@ -238,7 +238,7 @@ def collect_project(
         project_renderer: Optional[DbtProjectYamlRenderer] = None,
     ) -> Union[Project, PartialProject]:
 
-        project_root = args.project_dir if args.project_dir else os.getcwd()
+        project_root = flags.PROJECT_DIR if flags.PROJECT_DIR else os.getcwd()
         version_check = bool(flags.VERSION_CHECK)
         partial = Project.partial_load(project_root, verify_version=version_check)
         if project_renderer is None:
diff --git a/core/dbt/flags.py b/core/dbt/flags.py
index b7f8ae95ef2..6535e8d1d7b 100644
--- a/core/dbt/flags.py
+++ b/core/dbt/flags.py
@@ -47,6 +47,7 @@
 CACHE_SELECTED_ONLY = None
 TARGET_PATH = None
 LOG_PATH = None
+PROJECT_DIR = None
 
 _NON_BOOLEAN_FLAGS = [
     "LOG_FORMAT",
@@ -56,6 +57,7 @@
     "TARGET_PATH",
     "LOG_PATH",
     "WARN_ERROR_OPTIONS",
+    "PROJECT_DIR",
 ]
 
 _NON_DBT_ENV_FLAGS = ["DO_NOT_TRACK"]
@@ -86,6 +88,7 @@
     "CACHE_SELECTED_ONLY": False,
     "TARGET_PATH": None,
     "LOG_PATH": None,
+    "PROJECT_DIR": None,
 }
 
 
@@ -137,7 +140,7 @@ def set_from_args(args, user_config):
     global WRITE_JSON, PARTIAL_PARSE, USE_COLORS, STORE_FAILURES, PROFILES_DIR, DEBUG, LOG_FORMAT
     global INDIRECT_SELECTION, VERSION_CHECK, FAIL_FAST, SEND_ANONYMOUS_USAGE_STATS
     global PRINTER_WIDTH, WHICH, LOG_CACHE_EVENTS, QUIET, NO_PRINT, CACHE_SELECTED_ONLY
-    global TARGET_PATH, LOG_PATH
+    global TARGET_PATH, LOG_PATH, PROJECT_DIR
 
     STRICT_MODE = False  # backwards compatibility
     # cli args without user_config or env var option
@@ -168,6 +171,7 @@ def set_from_args(args, user_config):
     CACHE_SELECTED_ONLY = get_flag_value("CACHE_SELECTED_ONLY", args, user_config)
     TARGET_PATH = get_flag_value("TARGET_PATH", args, user_config)
     LOG_PATH = get_flag_value("LOG_PATH", args, user_config)
+    PROJECT_DIR = get_flag_value("PROJECT_DIR", args, user_config)
 
     _set_overrides_from_env()
 
@@ -267,6 +271,7 @@ def get_flag_dict():
         "cache_selected_only": CACHE_SELECTED_ONLY,
         "target_path": TARGET_PATH,
         "log_path": LOG_PATH,
+        "project_dir": PROJECT_DIR,
     }
 
 
diff --git a/core/dbt/task/base.py b/core/dbt/task/base.py
index 63449de10c7..399d30256d5 100644
--- a/core/dbt/task/base.py
+++ b/core/dbt/task/base.py
@@ -119,10 +119,10 @@ def interpret_results(self, results):
 def get_nearest_project_dir(args):
     # If the user provides an explicit project directory, use that
     # but don't look at parent directories.
-    if args.project_dir:
-        project_file = os.path.join(args.project_dir, "dbt_project.yml")
+    if flags.PROJECT_DIR:
+        project_file = os.path.join(flags.PROJECT_DIR, "dbt_project.yml")
         if os.path.exists(project_file):
-            return args.project_dir
+            return flags.PROJECT_DIR
         else:
             raise dbt.exceptions.DbtRuntimeError(
                 "fatal: Invalid --project-dir flag. Not a dbt project. "
diff --git a/core/dbt/task/debug.py b/core/dbt/task/debug.py
index 5f3e3854759..014265b9d8e 100644
--- a/core/dbt/task/debug.py
+++ b/core/dbt/task/debug.py
@@ -66,8 +66,8 @@ def __init__(self, args, config):
         except dbt.exceptions.Exception:
             # we probably couldn't find a project directory. Set project dir
             # to whatever was given, or default to the current directory.
-            if args.project_dir:
-                self.project_dir = args.project_dir
+            if flags.PROJECT_DIR:
+                self.project_dir = flags.PROJECT_DIR
             else:
                 self.project_dir = os.getcwd()
         self.project_path = os.path.join(self.project_dir, "dbt_project.yml")
diff --git a/test/unit/test_flags.py b/test/unit/test_flags.py
index 6f03ec22e92..0f20df28d40 100644
--- a/test/unit/test_flags.py
+++ b/test/unit/test_flags.py
@@ -280,6 +280,19 @@ def test__flags(self):
         os.environ.pop('DBT_LOG_PATH')
         delattr(self.args, 'log_path')
 
+        # project_dir
+        flags.set_from_args(self.args, self.user_config)
+        self.assertIsNone(flags.PROJECT_DIR)
+        os.environ['DBT_PROJECT_DIR'] = 'a/b/c'
+        flags.set_from_args(self.args, self.user_config)
+        self.assertEqual(flags.PROJECT_DIR, 'a/b/c')
+        setattr(self.args, 'project_dir', 'd/e/f')
+        flags.set_from_args(self.args, self.user_config)
+        self.assertEqual(flags.PROJECT_DIR, 'd/e/f')
+        # cleanup
+        os.environ.pop('DBT_PROJECT_DIR')
+        delattr(self.args, 'project_dir')
+
     def test__flags_are_mutually_exclusive(self):
         # options from user config
         self.user_config.warn_error = False